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<!-- saved from url=(0055)https://alienbill.com/2600/101/docs/stella.html#ednotes -->
<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>
Stella Programmer's Guide (Unofficial HTML version)
</title>
</head>
<body>
<center>
<h2>
STELLA<br>
PROGRAMMER'S<br>
GUIDE<br>
</h2>
by Steve Wright 12/03/79<p>
Reconstructed by Charles Sinnett 6/11/93<br>
Email: cas@mentor.cc.purdue.edu</p><p>
HTMLified by B. Watson 9/14/2001<br>
Email: atari@hardcoders.org<br>
<i><a href="https://alienbill.com/2600/101/docs/stella.html#ednotes">(Editor's notes --BW)</a></i>
</p></center>
<p>
</p><h3>TABLE OF CONTENTS</h3>
<ul>
<li>
<a href="https://alienbill.com/2600/101/docs/stella.html#tvprot">TELEVISION PROTOCOL</a>
<ul>
<li>
<a href="https://alienbill.com/2600/101/docs/diagram1.gif">Diagram 1 - Atari TV Frame</a>
</li></ul>
</li><li><a href="https://alienbill.com/2600/101/docs/stella.html#tiaprog">The TIA (as seen by the programmer)</a>
<ul>
<li>
<a href="https://alienbill.com/2600/101/docs/stella.html#tiaprog1.0">1.0 General Description</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#tiaprog2.0">2.0 The Registers</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#tiaprog3.0">3.0 Synchronization</a>
<ul>
<li>
<a href="https://alienbill.com/2600/101/docs/stella.html#tiaprog3.1">3.1 Horizontal Timing</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#tiaprog3.2">3.2 Microprocessor Synchronization</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#tiaprog3.3">3.3 Vertical timing</a>
</li></ul>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#tiaprog4.0">4.0 Color and Luminosity</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#tiaprog5.0">5.0 Playfield</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#tiaprog6.0">6.0 The Moveable Objects Graphics</a>
<ul>
<li>
<a href="https://alienbill.com/2600/101/docs/stella.html#tiaprog6.1">6.1 Missile Graphics (M0, M1)</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#tiaprog6.2">6.2 Ball Graphics (BL)</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#tiaprog6.3">6.3 Player Graphics (P0, P1)</a>
</li></ul>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#tiaprog7.0">7.0 Horizontal Positioning</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#tiaprog8.0">8.0 Horizontal Motion</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#tiaprog9.0">9.0 Object Priorities</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#tiaprog10.0">10.0 Collisions</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#tiaprog11.0">11.0 Sound</a>
<ul>
<li>
<a href="https://alienbill.com/2600/101/docs/stella.html#tiaprog11.1">11.1 Tone</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#tiaprog11.2">11.2 Frequency</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#tiaprog11.3">11.3 Volume</a>
</li></ul>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#tiaprog12.0">12.0 Input Ports</a>
<ul>
<li>
<a href="https://alienbill.com/2600/101/docs/stella.html#tiaprog12.1">12.1 Dumped Input Ports (INPT0 thru INPT3)</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#tiaprog12.2">12.2 Latched Input Ports (INPT4, INPT5)</a>
</li></ul>
</li></ul>
</li><li>
THE PIA (6532)
<ul>
<li>
<a href="https://alienbill.com/2600/101/docs/stella.html#pia1.0">1.0 General</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#pia2.0">2.0 Interval timer</a>
<ul>
<li>
<a href="https://alienbill.com/2600/101/docs/stella.html#pia2.1">2.1 Setting the timer</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#pia2.2">2.2 Reading the timer</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#pia2.3">2.3 When the timer reaches zero</a>
</li></ul>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#pia3.0">3.0 RAM</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#pia4.0">4.0 The I/O ports</a>
<ul>
<li>
<a href="https://alienbill.com/2600/101/docs/stella.html#pia4.1">4.1 Port B - Console Switches (read only)</a>
</li></ul>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#pia5.0">5.0 Port A - Hand Controllers</a>
<ul>
<li>
<a href="https://alienbill.com/2600/101/docs/stella.html#pia5.1">5.1 Setting for input or output</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#pia5.2">5.2 Inputting and Outputting</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#pia5.3">5.3 Joystick Controllers</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#pia5.4">5.4 Paddle (pot) controllers</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#pia5.5">5.5 Keyboard controllers</a>
</li></ul>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#pia6.0">6.0 Address summary table</a>
</li></ul>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#palsecam">PAL/SECAM CONVERSIONS</a>
<ul>
<li>
PAL
</li><li>
SECAM
</li></ul>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#tia1a">
TIA 1A - TELEVISION INTERFACE ADAPTOR (MODEL 1A)</a>
<ul>
<li>
<a href="https://alienbill.com/2600/101/docs/stella.html#tia1agen">
GENERAL DESCRIPTION</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#tia1adet">
DETAILED DESCRIPTION</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#tia1a1">1. Data and addressing</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#tia1a2">2. Synchronization</a>
<ul>
<li>
A. Horizontal Timing
</li><li>
B. Vertical Timing
</li><li>
C. Composite Sync
</li><li>
D. Microprocessor Synchronization
</li></ul>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#tia1a3">3. Playfield graphics Register</a>
<ul>
<li>
A. Description
</li><li>
B. Normal Serial Output
</li><li>
C. Reflected Serial Output
</li><li>
D. Timing Constraints
</li></ul>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#tia1a4">4. Horizontal Position Counters</a>
<ul>
<li>
A. Description
</li><li>
B. Ball position Counter
</li><li>
C. Player Position Counters
</li><li>
D. Missile Position Counters
</li></ul>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#tia1a5">5. Horizontal Motion Registers</a>
<ul>
<li>
A. General Description
</li><li>
B. Timing constraints
</li></ul>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#tia1a6">6. Moving Object Graphics Registers</a>
<ul>
<li>
A. General Description
</li><li>
B. Missile Graphics
</li><li>
C. Player Graphics
</li><li>
D. Vertical Delay
</li><li>
E. Ball Graphics
</li></ul>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#tia1a7">7. Collision Detection Latches</a>
<ul>
<li>
A. Definitions
</li><li>
B. Reading Collision
</li><li>
C. Reset
</li></ul>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#tia1a8">8. Input ports</a>
<ul>
<li>
A. General Description
</li><li>
B. Dumped Input Ports (I0 through I3)
</li><li>
C. Latched Input ports (I4, I5)
</li></ul>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#tia1a8.5">8.5 Priority Encoder</a>
<ul>
<li>
A. Purpose
</li><li>
B. Priority Assignment
</li><li>
C. Priority Control
</li></ul>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#tia1a9">9. Color Luminance Registers</a>
<ul>
<li>
A. Description
</li><li>
B. Multiplexing
</li></ul>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#tia1a10">10. Color Phase Shifter</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#tia1a11">11. Audio Circuits</a>
<ul>
<li>
A. Frequency Select
</li><li>
B. Noise-Tone Generator
</li><li>
C. Volume Select
</li></ul>
</li></ul>
<i>(These images are links to external files. --BW)</i>
<ul>
<li>
<a href="https://alienbill.com/2600/101/docs/figure1.gif">Figure 1. Vertical Delay</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/figure2.gif">Figure 2. Synchronization<br>
Figure 3. Color-Luminance</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/figure4.gif">Figure 4. Typical Horizontal Motion Circuit</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/figure5.gif">Figure 5. Playfield Graphics</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/figure6.gif">Figure 6. Collision Detection</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/figure7.gif">Figure 7. Audio Circuit</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/figure8.gif">Figure 8. Input Ports</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/figure9.gif">Figure 9. Game System</a>
</li></ul>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#W">Write Address Detailed Functions</a>
<ul>
<li>
<a href="https://alienbill.com/2600/101/docs/stella.html#WSYNC">WSYNC (wait for sync)</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#RSYNC">RSYNC (reset sync)</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#VSYNC">VSYNC</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#VBLANK">VBLANK</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#PJ">PF0 (PF1, PF2)</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#PLAYFIELD">PLAYFIELD REGISTERS SERIAL OUTPUT</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#CTRLPF">CTRLPF</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#NUSIZ">NUSIZ0 (NUSIZ1)</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#RESP">RESP0 (RESP1, RESM0, RESM1, RESBL)</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#RESMP">RESMP0 (RESMP1)</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#HMOVE">HMOVE</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#HMCLR">HMCLR</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#HMP">HMP0 (HMP1, HMM0, HMM1, HMBL)</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#ENAM">ENAM0 (ENAM1, ENABL)</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#GRP">GRP0 (GRP1)</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#REFP">REFP0 (REFP1)</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#VDELP">VDELP0 (VDELP1, VDELBL)</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#CXCLR">CXCLR</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#COLUP">COLUP0 (COLUP1, COLUPF, COLUBK)</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#AUDF">AUDF0 (AUDF1)</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#AUDC">AUDC0 (AUDC1)</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#AUDV">AUDV0 (AUDV1)</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#wsummary">WRITE ADDRESS SUMMARY</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/stella.html#rsummary">READ ADDRESS SUMMARY</a>
</li></ul>
<hr>
<i>(These documents are in separate files, to help speed
loading of this page... Ghods know it already takes forever! --BW)</i>
<ul>
<li>
<a href="https://alienbill.com/2600/101/docs/diagram2.gif">
TIA O0..02 AND LUM TIMING</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/diagram3.gif">
TIA WRITE TIMING CHARACTERISTICS</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/diagram4.gif">
TIA READ TIMING CHARACTERISTICS</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/diagram5.gif">
TIA COMP-SYN AND READY TIMING</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/diagram6.gif">
RSYNC, RES0O, H01, H02, SHB, 02, 0O</a>
</li><li>
<a href="https://alienbill.com/2600/101/docs/diagram7.gif">
TIA RSYNC AND BLANK AND READY TIMING</a>
</li></ul>
</li></ul>
<hr>
<a name="tvprot"></a>
<h3>TELEVISION PROTOCOL</h3><p>
(The TV picture according to Atari)<br>
</p><blockquote>
For the purposes of Stella programming, a single television "frame" consists
of 262 horizontal lines, and each line is divided by 228 clock counts
(3.58MHz). The actual TV picture is drawn line by line from the top down
60 times a second, and actaully consists of only a portion of the entire
"frame" (see diag. #1). A typical frame will consists of 3 vertical sync
(VSYNC) lines*, 37 vertical blank (VBLANK) lines, 192 TV picture lines,
and 30 overscan lines. Atari's research has shown that this pattern will
work on all types of TV sets. Each scan lines starts with 68 clock counts of
horizontal blank (not seen on the TV screen) followed by 160 clock counts to
fully scan one line of TV picture. When the electron beam reaches the end
of a scan line, it returns to the left side of the screen, waits for the 68
horizontal blank clock counts, and proceeds to draw the next line below.
<p>
All horizontal timing is taken care of by hardware, but the microprocessor
must "manually" control vertical timing to signal the start of the next
frame. When the last line of the previous frame is detected, the
microprocessor must generate 3 lines of VSYNC, 37 lines of VBLANK, 192
lines of actual TV picture, and 30 lines of overscan. Fortunately, both
VSYNC and VBLANK can simply be turned on and off at the appropriate
times, freeing the microprocessor for other activities during their execution.
</p><p>
* (to signal the TV set to start a new frame)
</p><p>
The actual TV picture is drawn one line at a time by having the
microprocessor enter the data for that line into the Television Interface
Adaptor (TIA) chip, which then converts the data into video signals. The
TIA can only have data in it that pertains to the line being currently drawn,
so the microprocessor must be "one step ahead" of the electron beam on each
line. Since one microprocessor machine cycle occurs every 3 clock counts,
the programmer has only 76 machine cycles per line (228/3 = 76) to
construct the actual picture (actually less because the microprocessor must
be ahead of the raster). To allow more time for the software, it is customary
(but not required) to update the TIA every two scan lines. The portion of
the program that constructs this TV picture is referred to as the "Kernel", as
it is the essence or kernel of the game.
</p><p>
In general, the remaining 70 scan lines (3 for VSYNC, 37 for VBLANK, and
30 for overscan) will provides 5,320 machine cycles (70 lines x 76 machine
cycles) for housekeeping and game logic. Such activities as calculating the
new position of a player, updating the score, and checking for new inputs
are typically done during this time.
</p><p>
<a href="https://alienbill.com/2600/101/docs/diagram1.gif">Diagram 1 - Atari TV Frame</a>
</p></blockquote>
<hr>
<a name="tiaprog"></a>
<h3>The TIA (as seen by the programmer)</h3><p>
<a name="tiaprog1.0"></a>
1.0 General Description</p><p>
</p><blockquote>
The TIA is a custom IC designed to create the TV picture and sound from
the instructions sent to it by the microprocessor. It converts the 8 bit
parallel data from the microprocessor into signals that are sent to video
modulation circuits which combine and shape those signals to be compatible
with ordinary TV reception. A "playfield" and 5 moveable objects can be
created and manipulated by software.
<p>
A playfield consisting of walls, clouds, barriers, and other seldom moved
objects can be created over a colored background. The 5 moveable objects
can be positioned anywhere, and consists of 2 players, 2 missiles, and a ball.
The playfield, players, missiles, and ball are created and manipulated by a
series of registers in the TIA that the microprocessor can address and write
into. Each type of object has certain defined capabilities. For example, a
player can be moved with one instruction, but the playfield must be
completely re-drawn in order to make it "move".
</p><p>
Color and luminosity (brightness) can be assigned to the background,
playfield, and 5 moveable objects. Sound can also be generated and
controlled for volume, pitch, and type of sound. Collisions between the
various objects on the TV screen are detected by the TIA and can be read by
the microprocessor . Input ports which can be read by the microprocessor
give the status of some of the various hand held controllers.
</p><p>
</p></blockquote>
<a name="tiaprog2.0"></a>
2.0 The Registers
<p>
</p><blockquote>
All instructions to the TIA are achieved by addressing and writing to
various registers in the chip. A key point to remember is data written in a
register is latched an retained until altered by another write operation into
that register. For example, if the color register for a player is set for red,
that player will be red every time it is drawn until that color register is
changed. All of the registers are addressed by the microprocessor as part of
the overall RAM/ROM memory space.
<p>
All registers have fixed address locations and pre-assigned address names for handy
reference. Many registers do not use all 8 data bits, and some registers are used to
"strobe" or trigger events. A "strobe" register executes its function the instant it is
written to (the data written is ignored). The only registers the microprocessor can read
are the collision registers and input port registers. These registers are conveniently
arranged so that the data bits of interest always appear as data bits 6 or 7 for easy access.
</p><p>
</p></blockquote>
<a name="tiaprog3.0"></a>
3.0 Synchronization<p>
</p><p>
</p><blockquote>
<a name="tiaprog3.1"></a>
3.1 Horizontal Timing
<blockquote>
When the electron beam scans across the TV screen and reaches the right
edge, it must be turned off and moved back to the left edge of the screen to
begin the next scan line. The TIA takes care of this automatically,
independent of the microprocessor. A 3.58 MHz oscillator generates clock
pulses called "color clocks" which go into a pulse counter in the TIA. This
counter allows 160 color clocks for the beam to reach the right edge, then
generates a horizontal sync signal (HSYNC) to return the beam to the left
edge. It also generates the signal to turn the beam off (horizontal blanking)
during its return time of 68 color clocks. Total round trip for the electron
beam is 160 + 68 = 228 color clocks. Again, all the horizontal timing is
taken care of by the TIA without assistance from the microprocessor.
<p>
</p></blockquote>
<a name="tiaprog3.2"></a>
3.2 Microprocessor Synchronization
<blockquote>
The microprocessor's clock is the 3.58 MHz oscillator divided by 3, so one
machine cycle is 3 color clocks. Therefore, one complete scan line of 228
color clocks allows only 76 machine cycles (228/3 = 76) per scan line. The
microprocessor must be synchronized with the TIA on a line-by-line basis,
but program loops and branches take unpredictable lengths of time. To
solve this software sync. problem, the programmer can use the <a href="https://alienbill.com/2600/101/docs/stella.html#WSYNC">WSYNC</a>
(Wait for SYNC) strobe register. Simply writing to the WSYNC causes the
microprocessor to halt until the electron beam reaches the right edge of the
screen, then the microprocessor resumes operation at the beginning of the
68 color clocks for horizontal blanking. Since the TIA latches all
instructions until altered by another write operation, it could be updated
every 2 or 3 lines. The advantage is the programmer gains more time to
execute software, but at a price paid with lower vertical resolution in the
graphics.
<p>
NOTE: WSYNC and all the following addresses' bit structures are itemized
in the TIA hardware manual. The purpose of this document is to make
them understandable.
</p><p>
</p></blockquote>
<a name="tiaprog3.3"></a>
3.3 Vertical timing
<blockquote>
When the electron beam has scanned 262 lines, the TV set must be signaled
to blank the beam and position it at the top of the screen to start a new
frame. This signal is called vertical sync, and the TIA must transmit this
signal for at least 3 scan lines. This is accomplished by writing a "1" in D1
of <a href="https://alienbill.com/2600/101/docs/stella.html#VSYNC">VSYNC</a> to turn it on, count at least 2 scan lines, then write a "0" to D1 of
VSYNC to turn it off.
<p>
To physically turn the beam off during its repositioning time, the TV set
needs 37 scan lines of vertical blanks signal from the TIA. This is
accomplished by writing a "1" in D1 of <a href="https://alienbill.com/2600/101/docs/stella.html#VBLANK">VBLANK</a> to turn it on, count 37
lines, then write a "0" to D1 of VBLANK to turn it off. The microprocessor
is of course free to execute other software during the vertical timing
commands, VSYNC and VBLANK.
</p><p>
</p></blockquote>
</blockquote>
<a name="tiaprog4.0"></a>
4.0 Color and Luminosity
<p>
</p><blockquote>
Color and luminosity can be assigned to the background (BK), playfield
(PF), ball (BL), player 0 (P0), player 1(P1), missile 0 (M0), and missile 1
(M1). There are only four color-lum registers for these 7 objects, so the
objects are paired to share the same register according to the following list:
<p>
</p><blockquote>
<table border="1">
<tbody><tr>
<td>color-lum register</td> <td>Objects colored</td></tr>
<tr><td>COLUMP0</td> <td>P0, M0 (player 0, missile 0)</td></tr>
<tr><td>COLUMP1</td> <td>P1, M1 (player 1, missile 1)</td></tr>
<tr><td>COLUMPF</td> <td>PF, BL (playfield, ball)</td></tr>
<tr><td>COLUMBK</td> <td>BK (background)</td></tr>
</tbody></table>
</blockquote>
<p>
For example, if the <a href="https://alienbill.com/2600/101/docs/stella.html#COLUP">COLUMP0</a> register is set for light red, both P0 and M0
will be light red when drawn.
</p><p>
A color-lum register is set for both color and luminosity by writing a single 7
bit instruction to that register. Four of the bits select one of the 16
available colors, and the other 3 bits select one of 8 levels of luminosity
(brightness). The specific codes required to create specific color and lum are
listed in the Detailed Address List of the TIA hardware manual. As with all
registers (except the "strobe" registers), the data written to them is latched
until altered by another write operation.
</p><p>
<i>(These registers are referred to here as COLUMxx, but everywhere else
they are COLUxx, including later in this document. --BW)</i>
</p></blockquote>
<a name="tiaprog5.0"></a>
5.0 Playfield
<p>
</p><blockquote>
The <a href="https://alienbill.com/2600/101/docs/stella.html#PF">PF</a> register is used to create a playfield of walls, clouds, barriers, etc., that are
seldom moved. This low resolution register is written into to draw the left half of the
TV screen only. The right half of the screen is drawn by software selection of whether a
duplication or a reflection of the right half.
<p>
The PF register is 20 bits wide, so the 20 bits are written into 3 addresses:
PF0, PF1, and PF2. PF0 is only 4 bits wide and constructs the first 4 "bits"
of the playfield, starting at the left edge of the TV screen. PF1 constructs
the next 8 "bits", and PF2 the last 8 bits" which end at the center of the
screen. The PF register is scanned from left to right and where a "1" is
found the PF color is drawn, and where a "0" is found, the BK color is
drawn. To clear the playfield, obviously zeros must be written into PF0,
PF1, and PF2.
</p><p>
To make the right half of the playfield into a duplication or copy of the left
half, a "0" is written to D0 of the <a href="https://alienbill.com/2600/101/docs/stella.html#CTRLPF">CTLPF</a> (control playfield) register.
Writing a "1" will cause the reflection to be displayed.
</p></blockquote>
<p>
<a name="tiaprog6.0"></a>
6.0 The Moveable Objects Graphics
</p><blockquote>
<p>
All 5 moveable objects (P0, M0, P1, M1, BL) can be assigned a horizontal
location on the screen and moved left or right relative to their location.
Vertical positions, however, are treated in an entirely different manner. In
principle, these objects appear at whatever scan lines their graphics
registers are enabled. For example, let us assume the ball is to be
positioned vertically in the center of the screen. The screen has 192 scan
lines and we want the ball to be 2 scan lines "thick". The ball graphics
would be disabled until scan line 96, enabled for 2 scan lines, then disabled
for the rest of the frame. Each type of object (players, missiles, and ball)
has its own characteristics and limitations.
</p><p>
</p></blockquote>
<a name="tiaprog6.1"></a>
6.1 Missile Graphics (M0, M1)
<blockquote>
The two missile graphics registers will draw a missile on any scan line by
writing a "1" to the one bit enable missile registers (<a href="https://alienbill.com/2600/101/docs/stella.html#ENAM">ENAM0</a>, ENAM1).
Writing a "0" to these registers will disable the graphics. The missiles' left
edge is positioned by a horizontal position register, but the right edge is a
function of how wide the missile is make. Width of a missile is controlled by
writing into bits D4 and D5 of the number-size registers (<a href="https://alienbill.com/2600/101/docs/stella.html#NUSIZ">NUSIZ0</a>,
NUSIZ1). This has the effect of "stretching" the missile out over 1,2,4, or 8
color clock counts (a full scan line is 160 color clocks).
<p>
</p></blockquote>
<a name="tiaprog6.2"></a>
6.2 Ball Graphics (BL)
<blockquote>
The ball graphics register works just like the missile registers. Writing a
"1" to the enable ball register (<a href="https://alienbill.com/2600/101/docs/stella.html#ENABL">ENABL</a>) enables the ball graphics until the
register is disabled. The ball can also be "stretched" to widths of 1, 2, 4, or 8
color clock counts by writing to bits D4 and D5 of the <a href="https://alienbill.com/2600/101/docs/stella.html#CTRLPF">CTRLPF</a> register.
<p>
The ball can also be vertically delayed one can line. For example, if the ball
graphics were enabled on scan line 95, it could be delayed to not display on
the screen until scan line 96 by writing a "1" to D0 of the vertical delay
(<a href="https://alienbill.com/2600/101/docs/stella.html#VDELP">VDELBL</a>) register. The reason for having a vertical delay capability is
because most programs will update the TIA every 2 lines. This confines all
vertical movements of objects to 2 scan line "jumps". The use of vertical
delay allows the objects to move one scan line at a time.
</p><p>
</p></blockquote>
<a name="tiaprog6.3"></a>
6.3 Player Graphics (P0, P1)
<blockquote>
The player graphics are the most sophisticated of all the moveable objects.
They have all the capabilities of the missile and ball graphics, plus three
move capabilities. Players can take on a "shape" such as a man or an
airplane, and the player can easily be flipped over horizontally to display
the mirror image (reflection) instead of the original image, plus multiple
copies of the players can be created.
<p>
The player graphics are drawn line-by-line like all other graphics. The
difference here is each scan line of the player is 8 "bits" wide, whereas the
missiles and ball are one "bit" wide. Therefore, a player can be though of as
being drawn of graph paper 8 squares wide and as tall as desired. To "color
in the squares" of this imaginary graph paper, 8 data bits are written into
the players graphics registers (<a href="https://alienbill.com/2600/101/docs/stella.html#GRP">GP0</a>, GP1). This 8 bit register is scanned
from D7 to D0, and wherever a "1" is found that "square" gets the players'
color (from the color-lum register) and where a "0" is found that "square"
gets the background color. To position a player vertically, simply leave all
"0's" in the graphics registers (GP0, GP1) until the electron beam is on the
scan line desired, write to the graphics register line-by-line describing the
player, then write all "0's" to turn off the players' graphics until the end of
that frame.
</p><p>
To display a mirror image (reflection) instead of the original figure, write a
"1" to D3 of the one bit reflection register (<a href="https://alienbill.com/2600/101/docs/stella.html#REFP">REFP0</a>, REFP1). A "0" written to
these registers restores the original figure.
</p><p>
Multiple copies of players as well as their size are controlled by writing 3
bits (D0, D1, D2) into the number-size registers (<a href="https://alienbill.com/2600/101/docs/stella.html#NUSIZ">NUSIZ0</a>, NUSIZ1). These
three bits select from 1 to 3 copies of the player, spacing of those copies, as
well as the size of the player (each "square" of the player can be 1, 2, or 4
clocks wide). Whenever multiple copies are selected, the TIA automatically
creates the same number of copies of the missile for that player. Again, the
specifics of all this are laid out in the TIA hardware manual.
</p><p>
Vertical delay for the players works exactly like the ball by writing a "1" to
D0 in the players' vertical delay registers (<a href="https://alienbill.com/2600/101/docs/stella.html#VDELP">VDELP0</a>, VDELP1). Writing a
"0" to these locations disables the vertical delay.
</p><p>
</p></blockquote>
<a name="tiaprog7.0"></a>
7.0 Horizontal Positioning
<blockquote>
<p>
The horizontal position of each object is set by writing to its associated reset
register (<a href="https://alienbill.com/2600/101/docs/stella.html#RESP">RESP0</a>, RESP1, <a href="https://alienbill.com/2600/101/docs/stella.html#RESM">RESM0</a>, RESM1, <a href="https://alienbill.com/2600/101/docs/stella.html#RESBL">RESBL</a>) which are all "strobe"
registers (they trigger their function as soon as they are addressed). That
causes the object to be positioned wherever the electron bean was in its
sweep across the screen when the register was reset. for example, if the
electron beam was 60 color clocks into a scan line when RESP0 was written
to, player 0 would be positioned 60 color clocks "in" on the next scan line.
Whether or not P0 is actually drawn on the screen is a function of the data
in the <a href="https://alienbill.com/2600/101/docs/stella.html#GRP">GP0</a> register, but if it were drawn, it would show up at 60. Resets to
these registers anywhere during horizontal blanking will position objects at
the left edge of the screen (color clock 0). Since there are 3 color clocks per
machine cycle, and it can take up to 5 machine cycles to write the register,
the programmer is confined to positioning the objects at 15 color clock
intervals across the screen. This "course" positioning is "fine tuned" by the
Horizontal Motion, explained in section 8.0.
</p><p>
Missiles have an additional positioning command. Writing a "1" to D1 of
the reset missile-to-player register (<a href="https://alienbill.com/2600/101/docs/stella.html#RESMP">RESMP0</a>, RESMP1) disables that
missiles' graphics (turns it off) and repositions it horizontally to the center
of its associated player. Until a "0" is written to the register, the missile's
horizontal position is locked to the center of its player in preparation to be
fired again.
</p><p>
</p></blockquote>
<a name="tiaprog8.0"></a>
8.0 Horizontal Motion
<blockquote>
<p>
Horizontal motion allows the programmer to move any of the 5 graphics
objects relative to their current horizontal position. Each object has a 4 bit
horizontal motion register (<a href="https://alienbill.com/2600/101/docs/stella.html#HMP">HMP0</a>, HMP1, <a href="https://alienbill.com/2600/101/docs/stella.html#HMM">HMM0</a>, HMM1, <a href="https://alienbill.com/2600/101/docs/stella.html#HMBL">HMBL</a>) that can
be loaded with a value in the range of +7 to -8 (negative values are
expressed in two's complement from). This motion is not executed until the
<a href="https://alienbill.com/2600/101/docs/stella.html#HMOVE">HMOVE</a> register is written to, at which time all motion registers move their
respective objects. Objects can be moved repeatedly by simply executing
HMOVE. Any object that is not to move must have a 0 in its motion
register. With the horizontal positioning command confined to positioning
objects at 15 color clock intervals, the motion registers fills in the gaps by
moving objects +7 to -8 color clocks. Objects can not be placed at any color
clock position across the screen. All 5 motion registers can be set to zero
simultaneously by writing to the horizontal motion clear register (<a href="https://alienbill.com/2600/101/docs/stella.html#HMCLR">HMCLR</a>).
</p><p>
There are timing constraints for the HMOVE command. The HMOVE
command must immediately follow a <a href="https://alienbill.com/2600/101/docs/stella.html#WSYNC">WSYNC</a> (Wait for SYNC) to insure the
HMOVE operation occurs during horizontal blanking. This is to allow
sufficient time for the motion registers to do their thing before the electron
beam starts drawing the next scan line. Also, for mysterious internal
hardware considerations, the motion registers should not be modified for at
least 24 machine cycles after an HMOVE command.
</p><p>
</p></blockquote>
<a name="tiaprog9.0"></a>
9.0 Object Priorities
<blockquote>
<p>
Each object is assigned a priority so when any two objects overlap the one
with the highest priority will appear to move in front of the other. To
simplify hardware logic, the missiles have the same priority as their
associated player, and the ball has the same priority as the playfield. The
background, of course, has the lowest priority. The following table
illustrates the normal (default) priority assignments.
</p><p>
</p><blockquote>
<table border="1">
<tbody><tr><td>Priority</td> <td>Objects</td></tr>
<tr><td>1</td> <td>P0, M0</td></tr>
<tr><td>2</td> <td>P1, M1</td></tr>
<tr><td>3</td> <td>BL, PF</td></tr>
<tr><td>4</td> <td>BK</td></tr>
</tbody></table>
</blockquote>
<p>
This priority assignment means that players and missiles will move in front
of the playfield. To make the players and missiles move behind the
playfield, a "1" must be written to D2 of the <a href="https://alienbill.com/2600/101/docs/stella.html#CTRLPF">CTRLPF</a> register. The
following table illustrates how the priorities are affected:
</p><p>
</p><blockquote>
<table border="1">
<tbody><tr><td>Priority</td> <td>Objects</td></tr>
<tr><td>1</td> <td>BL, PF</td></tr>
<tr><td>2</td> <td>P0, M0</td></tr>
<tr><td>3</td> <td>P1, M1</td></tr>
<tr><td>4</td> <td>BK</td></tr>
</tbody></table>
</blockquote>
<p>
One more priority control is available to be used for displaying the score.
When a "1" is written to D1 of the CTRLPF register, the left half of the
playfield takes on the color of player 0, and the right half the color of player
1. The game score can now be displayed using the <a href="https://alienbill.com/2600/101/docs/stella.html#PF">PF</a> graphics register, and
the score will be in the same color as its associated player.
</p><p>
</p></blockquote>
<a name="tiaprog10.0"></a>
10.0 Collisions
<blockquote>
<p>
The TIA detects collisions between any of the 6 objects it generates (the
playfield and 5 moveable objects). There are 15 possible two-object
collisions which are stored in 15 one bit latches. Each collision register
contains two of these latches which are read by the microprocessor on D6
and D7 of the data bus for easy access. A "1" on the data line indicates the
collision it records has occurred. The collision registers could be read at any
time but is usually done during vertical blank after all possible collisions
have occurred. The collision registers are all reset simultaneously by
writing to the collision reset register (<a href="https://alienbill.com/2600/101/docs/stella.html#CXCLR">CXCLR</a>).
</p><p>
</p></blockquote>
<a name="tiaprog11.0"></a>
11.0 Sound
<blockquote>
<p>
There are two audio circuits for generating sound. They are identical but
completely independent and can be operated simultaneously to produce
sound effects through the TV speaker. Each audio circuit has three
registers that control a noise-tone generator (what kind of sound), a
frequency selection (high or low pitch of the sound), and a volume control.
</p><p>
<a name="tiaprog11.1"></a>
11.1 Tone
</p><blockquote>
The noise-tone generator is controlled by writing to the 4 bit audio control
registers (<a href="https://alienbill.com/2600/101/docs/stella.html#AUDC">AUDC0</a>, AUDC1). The values written cause different kinds of
sounds to be generated. Some are pure tones like a flute, others have
various "noise" content like a rocket motor or explosion. Even though the
TIA hardware manual lists the sounds created by each value, some
experimentation will be necessary to find "your sound".
<p>
</p></blockquote>
<a name="tiaprog11.2"></a>
11.2 Frequency
<blockquote>
Frequency selection is controlled by writing to a 5 bit audio frequency
register (<a href="https://alienbill.com/2600/101/docs/stella.html#AUDF">AUDF0</a>, AUDF1). The value written is used to divide a 30KHz
reference frequency creating higher or lower pitch of whatever type of sound
is created by the noise-tone generator. By combining the pure tones
available from the noise-tone generator with frequency selection a wide
range of tones can be generated.
<p>
</p></blockquote>
<a name="tiaprog11.3"></a>
11.3 Volume
<blockquote>
Volume is controlled by writing to a 4 bit audio volume register (<a href="https://alienbill.com/2600/101/docs/stella.html#AUDV">AUDV0</a>,
AUDV1). Writing 0 to these registers turns sound off completely, and
writing any value up to 15 increases the volume accordingly.
<p>
</p></blockquote>
</blockquote>
<a name="tiaprog12.0"></a>
12.0 Input Ports
<blockquote>
<p>
There are six input ports whose logic states can be read on D7 by reading
the input port addresses (INPT0, thru INPT5). These six ports are divided
into two types, "dumped" and "latched".
</p><p>
<a name="tiaprog12.1"></a>
12.1 Dumped Input Ports (INPT0 thru INPT3)
</p><blockquote>
These four ports are used to read up to four paddle controllers. Each paddle controller
contains an adjustable pot controlled by the knob on the controller. The output of the
pot is used to charge a capacitor in the console, and when the capacitor is charged the
input port goes HI. The microprocessor discharges this capacitor by writing a "1" to D7
of <a href="https://alienbill.com/2600/101/docs/stella.html#VBLANK">VBLANK</a> then measures the time it takes to detect a logic one at that port. This
information can be used to position objects on the screen based on the position of the
knob on the paddle controller.
<p>
</p></blockquote>
<a name="tiaprog12.2"></a>
12.2 Latched Input Ports (INPT4, INPT5)
<blockquote>
These two ports have latches that are both enabled by writing a "1" or
disabled by writing a "0" to D6 of <a href="https://alienbill.com/2600/101/docs/stella.html#VBLANK">VBLANK</a>. When disabled the
microprocessor reads the logic level of the port directly. When enabled, the
latch is set for logic one and remains that way until its port goes LO. When
the port goes LO the latch goes LO and remains that way regardless of what
the port does. The trigger buttons of the joystick controllers connect to
these ports.
<p>
</p></blockquote>
</blockquote>
<hr>
<a name="pia"></a>
<h3>THE PIA (6532)</h3>
<p>
<a name="pia1.0"></a>
1.0 General
</p><p>
</p><blockquote>
The PIA chip is an off-the-shelf 6532 Peripheral Interface Adaptor which
has three functions: a programmable timer, 128 bytes of RAM, and two 8
bit parallel I/O ports.
<p>
</p></blockquote>
<a name="pia2.0"></a>
2.0 Interval timer
<blockquote>
<p>
The PIA uses the same clock as the microprocessor so that one PIA cycle
occurs for each machine cycle. The PIA can be set for one of four different
"intervals", where each interval is some multiple of the clock (and therefore
machine cycles). A value from 1 to 255 is loaded into the PIA which will be
decremented by one at each interval. The timer can now be read by the
microprocessor to determine elapsed time for timing various software
operations and keep them synchronized with the hardware (TIA chip).
</p><p>
<a name="pia2.1"></a>
2.1 Setting the timer
</p><blockquote>
The timer is set by writing a value or count (from 1 to 255) to the address of
the desired interval setting according to the following table :
<p>
</p><blockquote>
<table border="1">
<tbody><tr><td>Hex Address</td> <td>Interval</td> <td> Mnemonic</td></tr>
<tr><td>294</td> <td>1 clock</td> <td>TIM1T</td></tr>
<tr><td>295</td> <td>8 clocks</td> <td>TIM8T</td></tr>
<tr><td>296</td> <td>64 clocks</td> <td>TIM64T</td></tr>
<tr><td>297</td> <td>1024 clocks</td> <td>T1024T</td></tr>
</tbody></table>
</blockquote>
<p>
For example, if the value of 100 were written to TIM64T (HEX address 296)
the timer would decrement to 0 in 6400 clocks (64 clocks per interval x 100
intervals) which would also be 6400 microprocessor machine cycles.
</p><p>
</p></blockquote>
<a name="pia2.2"></a>
2.2 Reading the timer
<blockquote>
The timer may be read any number of times after it is loaded of course, but
the programmer is usually interested in whether or not the timer has
reached 0. The timer is read by reading INTIM at hex address 284.
<p>
</p></blockquote>
<a name="pia2.3"></a>
2.3 When the timer reaches zero
<blockquote>
The PIA decrements the value or count loaded into it once each interval
until it reaches 0. It holds that 0 counts for one interval, then the counter
flips to FF(HEX) and decrements once each clock cycle, rather than once per
interval. The purpose of this feature is to allow the programmer to
determine how long ago the timer zeroed out in the event the timer was
read after it passed zero.
</blockquote>
</blockquote>
<p>
<a name="pia3.0"></a>
3.0 RAM
</p><p>
</p><blockquote>
The PIA has 128 bytes of RAM located in the Stella memory map from HEX
address 80 to FF. The microprocessor stack is normally located from FF on
down, and variables are normally located from 80 on up (hoping the two
never meet).
<p>
</p></blockquote>
<a name="pia4.0"></a>
4.0 The I/O ports
<blockquote>
<p>
The two ports (Port A and Port B) are 8 bits wide and can be set for either
input or output. Port A is used to interface to carious hand-held controllers
but Port B is dedicated to reading the status of the Stella console switches.
</p><p>
<a name="pia4.1"></a>
4.1 Port B - Console Switches (read only)
</p><blockquote>
Port B is hardwired to be an input port only that is read by addressing
SWCHB (HEX 282) to determine the status of all the console switches
according to the following table:
<p>
</p><blockquote>
<table border="1">
<tbody><tr><td>Data Bit</td> <td>Switch</td> <td>Bit Meaning</td></tr>
<tr><td>D7</td> <td>P1 difficulty</td> <td>0 = amateur (B), 1 = pro (A)</td></tr>
<tr><td>D6</td> <td>P0 difficulty</td> <td>0 = amateur (B), 1 = pro (A)</td></tr>
<tr><td>D5/D4</td> <td colspan="2">(not used)</td></tr>
<tr><td>D3</td> <td>color - B/W</td> <td>0 = B/W, 1 = color</td></tr>
<tr><td>D2</td> <td colspan="2">(not used)</td></tr>
<tr><td>D1</td> <td>game select</td> <td>0 = switch pressed</td></tr>
<tr><td>D0</td> <td>game reset</td> <td>0 = switch pressed</td></tr>
</tbody></table>
</blockquote>
</blockquote>
<p>
</p></blockquote>
<a name="pia5.0"></a>
5.0 Port A - Hand Controllers
<blockquote>
<p>
Port A is under full software control to be configured as an input or an
output port. It can then be used to read or control various hand-head
controllers with the data bits defined differently depending on the type of
controller used.
</p><p>
<a name="pia5.1"></a>
5.1 Setting for input or output
</p><blockquote>
Port A has an 8 bit wide Data Direction Register (DDR) that is written to at
SWACNT (HEX 281) to set each individual pin of Port A to either input or
output. The Port A pins are labeled PA0 thru PA7, and writing a "0" to a
pins' DDR bit sets that pin as input, and a "1" sets it as an output. For
example, writing all 0's to SWACNT (the DDR for Port A) sets PA0 thru
PA7 (all 8 pins of Port A) as inputs. If F0 (11110000) were written to
SWACNT then PA7, PA6, PA5 &amp; PA4 would be outputs, and PA3, PA2, PA1
&amp; PA0 would be inputs.
</blockquote>
<p>
<a name="pia5.2"></a>
5.2 Inputting and Outputting
</p><blockquote>
Once the DDR has set the pins of Port A for input or output they may be
read or written to by addressing SWCHA (HEX 280).
</blockquote>
<p>
<a name="pia5.3"></a>
5.3 Joystick Controllers
</p><blockquote>
Two joysticks can be read by configuring the entire port as input and
reading the data at SWCHA according to the following table:
<p>
</p><blockquote>
<table border="1">
<tbody><tr><td>Data Bit</td><td>Direction</td><td>Player</td></tr>
<tr><td>D7</td><td>right</td><td>P0</td></tr>
<tr><td>D6</td><td>left</td><td>P0</td></tr>
<tr><td>D5</td><td>down</td><td>P0</td></tr>
<tr><td>D4</td><td>up</td><td>P0</td></tr>
<tr><td>D3</td><td>right</td><td>P1</td></tr>
<tr><td>D2</td><td>left</td><td>P1</td></tr>
<tr><td>D1</td><td>down</td><td>P1</td></tr>
<tr><td>D0</td><td>up</td><td>P1</td></tr>
</tbody></table>
(P0 = left player, P1 = right player)
<p>
</p></blockquote>
A "0" in a data bit indicates the joystick has been moved to close that
switch. All "1's" in a player's nibble indicates that joystick is not moving.
<p>
</p></blockquote>
<a name="pia5.4"></a>
5.4 Paddle (pot) controllers
<blockquote>
Only the paddle triggers are read from the PIA. The paddles themselves
are read at INP0 thru INPT3 of the TIA. The paddle triggers can be read at
SWCHA according to the following table :
<p>
</p><blockquote>
<table border="1">
<tbody><tr><td>Data Bit</td> <td>Paddle #</td></tr>
<tr><td>D7</td> <td>P0</td></tr>
<tr><td>D6</td> <td>P1</td></tr>
<tr><td>D5/D4</td> <td>(not used)</td></tr>
<tr><td>D3</td> <td>P2</td></tr>
<tr><td>D2</td> <td>P3</td></tr>
<tr><td>D1/D0</td> <td>(not used)</td></tr>
</tbody></table>
</blockquote>
<p>
</p></blockquote>
<a name="pia5.5"></a>
5.5 Keyboard controllers
<blockquote>
The keyboard controller has 12 buttons arranged into 4 rows and 3 columns.
A signal is sent to a row, then the columns are checked to see if a button is
pushed, then the next row is signaled and all columns sensed, etc. until the
entire keyboard is scanned and sensed. The PIA sends the signals to the
rows, and the columns are sensed by reading INPT0, INPT1, and INPT4 of
the TIA. With Port A configured as an output port, the data bits will send a
signal to the keyboard controller rows according to the following table :
<p>
</p><blockquote>
<table border="1">
<tbody><tr><td>Data Bit</td><td>Keyboard Row</td><td>Player</td></tr>
<tr><td>D7</td><td>bottom</td><td>P0</td></tr>
<tr><td>D6</td><td>third</td><td>P0</td></tr>
<tr><td>D5</td><td>second</td><td>P0</td></tr>
<tr><td>D4</td><td>top</td><td>P0</td></tr>
<tr><td>D3</td><td>bottom</td><td>P1</td></tr>
<tr><td>D2</td><td>third</td><td>P1</td></tr>
<tr><td>D1</td><td>second</td><td>P1</td></tr>
<tr><td>D0</td><td>top</td><td>P1</td></tr>
</tbody></table>
(P0 = left player, P1 = right player)
<p>
NOTE : a delay of 400 microseconds is necessary between writing to this
port and reading the TIA input ports.
</p></blockquote>
</blockquote>
</blockquote>
<p>
<a name="pia6.0"></a>
6.0 Address summary table
</p><p>
</p><blockquote>
<table border="1">
<tbody><tr><td>Hex Address</td> <td>Mnemonic</td> <td>Purpose</td></tr>
<tr><td>280</td> <td>SWCHA</td> <td>Port A; input or output (read or write)</td></tr>
<tr><td>281</td> <td>SWACNT</td> <td>Port A DDR, 0= input, 1=output</td></tr>
<tr><td>282</td> <td>SWCHB</td> <td>Port B; console switches (read only)</td></tr>
<tr><td>283</td> <td>SWBCNT</td> <td>Port B DDR (hardwired as input)</td></tr>
<tr><td>284</td> <td>INTIM</td> <td>Timer output (read only)</td></tr>
<tr><td>294</td> <td>TIM1T</td> <td>set 1 clock interval (838 nsec/interval)</td></tr>
<tr><td>295</td> <td>TIM8T</td> <td>set 8 clock interval (6.7 usec/interval)</td></tr>
<tr><td>296</td> <td>TIM64T</td> <td>set 64 clock interval (53.6 usec/interval)</td></tr>
<tr><td>297</td> <td>T1024T</td> <td>set 1024 clock interval (858.2 usec/interval)</td></tr>
</tbody></table>
<p>
NOTE: one clock is also one microprocessor machine cycle
</p></blockquote>
<hr>
<p>
<a name="palsecam"></a>
</p><h3>PAL/SECAM CONVERSIONS</h3>
<p>
PAL
</p><blockquote>
1. The number of scan lines, and therefore the frame time increases from
NTSC to PAL according to the following table:
<p>
</p><blockquote>
<table border="1" width="60%">
<tbody><tr>
<td colspan="3" align="right">NTSC</td>
<td colspan="2" align="right">PAL</td>
</tr>
<tr>
<td colspan="2" align="right">scanlines</td>
<td align="right">microseconds</td>
<td align="right">scanlines</td>
<td align="right">microseconds</td>
</tr>
<tr>
<td align="left" width="40%">VBLANK</td>
<td align="right" width="15%">40</td>
<td align="right" width="15%">2548</td>
<td align="right" width="15%">48</td>
<td align="right" width="15%">3085</td>
</tr>
<tr>
<td align="left" width="40%">KERNEL</td>
<td align="right">192</td>
<td align="right">12228</td>
<td align="right">228</td>
<td align="right">14656</td>
</tr>
<tr>
<td align="left" width="40%">OVERSCAN</td>
<td align="right">30</td>
<td align="right">1910</td>
<td align="right">36</td>
<td align="right">2314</td>
</tr>
<tr>
<td align="left" width="40%">FRAME</td>
<td align="right">262</td>
<td align="right">16686</td>
<td align="right">312</td>
<td align="right">20055</td>
</tr>
</tbody></table>
</blockquote>
<p>
2. Sounds will drop a little in pitch (frequency) because of a slower crystal
clock. Some sounds may need the <a href="https://alienbill.com/2600/101/docs/stella.html#AUDF">AUDF0</a>/AUDF1 touched up.
</p><p>
3. PAL operates at 50 Hz compared to NTSC 60Hz, a 17% reduction. If
game play speed is based on frames per second, it will slow down by 17%.
This can be disastrous for most skill/action carts. If the NTSC version is
designed with 2 byte fractional addition techniques (or anything not based
on frames per second) to move objects, then PAL conversion can be as
simple as changing the fraction tables, avoiding major surgery on the
program.
</p><p>
</p></blockquote>
SECAM
<blockquote>
1. SECAM is a little weird. It takes the PAL software, but the console
color/black &amp; white switch is hardwired as black &amp; white. Therefore, it
reads the PAL black &amp; white tables in software and assigns a fixed color to
each lum of black &amp; white according to the following table:
<p>
</p><blockquote>
<table border="1">
<tbody><tr><td>Lum</td> <td>Color</td></tr>
<tr><td>0</td> <td>Black</td></tr>
<tr><td>2</td> <td>Blue</td></tr>
<tr><td>4</td> <td>Red</td></tr>
<tr><td>6</td> <td>Magenta</td></tr>
<tr><td>8</td> <td>green</td></tr>
<tr><td>A</td> <td>cyan</td></tr>
<tr><td>C</td> <td>yellow</td></tr>
<tr><td>E</td> <td>white</td></tr>
</tbody></table>
</blockquote>
<p>
There is a trap here: the manual is the same for NTSC, PAL, &amp; SECAM.
This means that the descriptions for black &amp; white must jive between NTSC
&amp; PAL. If you make major changes to PAL black &amp; white to achieve good
SECAM color, NTSC black &amp; white must be made similar.
</p><p>
2. PAL sounds work fine on SECAM with one exception: when a sound is to
be turned off, it must be done by setting <a href="https://alienbill.com/2600/101/docs/stella.html#AUDV">AUDV0</a>/AUDV1 to 0, not by setting
<a href="https://alienbill.com/2600/101/docs/stella.html#AUDC">AUDC0</a>/AUDC1 to 0. Otherwise, you get an obnoxious background sound.
</p><p>
</p></blockquote>
<hr>
<a name="tia1a"></a>
<h3>TIA 1A - TELEVISION INTERFACE ADAPTOR (MODEL 1A)</h3>
<p>
<a name="tia1agen"></a>
GENERAL DESCRIPTION
</p><p>
</p><blockquote>
The TIA is an MOS integrated circuit designed to interface between an
eight (8) bit microprocessor and a television video modulator and to convert
eight (8) bit parallel data into serial outputs for the color, luminosity, and
composite sync required by a video modulator.
<p>
This circuit operates on a line by line basis, always outputting the same
information every television line unless new data is written into it by the
microprocessor.
</p><p>
A hardware sync counter produces horizontal sync timing independent of
the microprocessor. Vertical sync timing is supplied to this circuit by the
microprocessor and combined into composite sync.
</p><p>
Horizontal position counters are used to trigger the serial output of five (5)
horizontally movable objects; two players, two missiles and a ball. The
microprocessor can add or subtract from these position counters to move
these objects right or left.
</p><p>
The microprocessor determines all vertical position and motion by writing
zeros or ones into object registers before each appropriate horizontal line.
</p><p>
Walls, clouds and other seldom moved objects are produced by a low
resolution data register called the playfield register.
</p><p>
A fifteen (15) bit collision register detects all fifteen possible two object
collisions between these six (6) objects (five moveable and one playfield).
This collision register can be read and reset by the microprocessor. Six input
ports are also provided on this chip that can be read by the microprocessor.
These input ports and the collision register are the only chip addresses that
can be read by the microprocessor. All other addresses are write only.
</p><p>
Color luminosity registers are included that can be programmed by the
microprocessor with eight (8) luminosity and fifteen (15) color values. A
digital phase shifter is included on this chip to provide a single color output
with fifteen (15) phase angles.
</p><p>
Two (2) independent audio generating circuits are included, each with
programmable frequency, noise content, and volume control registers.
</p><p>
</p></blockquote>
<a name="tia1adet"></a>
DETAILED DESCRIPTION
<blockquote>
<p>
<a name="tia1a1"></a>
1. Data and addressing
</p><p>
</p><blockquote>
Registers on this chip are addressed by the microprocessor as part of its
overall RAM-ROM memory space. The attached table of read-write
addresses summarizes the addressable functions. There are no registers
that are both read and write. Some addresses however are both read and
write, with write data going into one register and read data returning from
a different register.
<p>
If the read-write line is low, the data bits indicated in this table will be
written into the addressed write location when the 02 clock goes from high
to low. Some registers are eight bits wide, some only one bit, and some
(strobes) have no bits, performing only control functions (such as resets)
when their address is written.
</p><p>
If the read-write line is high, the addressed location can be read by the
microprocessor on data lines 6 and 7 while the 02 clock is high.
</p><p>
The addresses given in the table refer only to the six (6) real address lines.
If any of the four (4) chip select lines are used for addressing, the addresses
must be modified accordingly.
</p><p>
</p></blockquote>
<a name="tia1a2"></a>
2. Synchronization
<blockquote>
<p>
A. Horizontal Timing
</p><blockquote>
A hardware counter on this chip produces all horizontal timing (such as
sync, blank, burst) independent of the microprocessor, This counter is
driven from an external 3.58 Mhz oscillator and has a total count of 228.
Blank is decoded as 68 counts and sync and color burst as 16 counts.
</blockquote>
<p>
B. Vertical Timing
</p><blockquote>
There are one bit, addressable registers on this chip for vertical sync and
vertical blank. The timing for these functions is established by the
microprocessor by writing zero or one into these bits. (<a href="https://alienbill.com/2600/101/docs/stella.html#VSYNC">VSYNC</a>, <a href="https://alienbill.com/2600/101/docs/stella.html#VBLANK">VBLANK</a> )
</blockquote>
<p>
C. Composite Sync
</p><blockquote>
Horizontal sync and the output of the vertical sync bit are combined
together to produce composite sync. This composite sync signal drives a
chip output pad to an external composite video resistor network.
</blockquote>
<p>
D. Microprocessor Synchronization
</p><blockquote>
The 3.58 MHz oscillator also clocks a divide by three counter on this chip
whose output (1.19 Mhz) is buffered to drive an output pad called 00. This
pad provides the input phase zero clock to the microprocessor which then
produces the system 02 clock (1.19 Mhz).
Software program loops require different lengths of time to run depending
on branch decisions made within the program. Additional synchronization
between the software and hardware. This is done with a one bit latch called
<a href="https://alienbill.com/2600/101/docs/stella.html#WSYNC">WSYNC</a> (wait for sync). When the microprocessor finishes a routine such
as loading registers for a horizontal line, or computing new vertical
locations during vertical blank, it can address WSYNC, setting this latch
high. When this latch is high, it drives an output pad to zero connected to
the microprocessor ready line (RDY). A zero on this line causes the
microprocessor to halt and wait. As shown in figure 2, WSYNC latch is
automatically reset to zero by the leading edge of the next horizontal blank
timing signal, releasing the RDY line, allowing the microprocessor to begin
its computation and register writing for this horizontal television line or
line pair.
<p>
</p></blockquote>
</blockquote>
<a name="tia1a3"></a>
3. Playfield graphics Register
<p>
</p><blockquote>
A. Description
<blockquote>
Objects such as walls, clouds, and score) which are not required to move, are
written into a 20 bit register called the playfield register. This register
(Figure 5) is loaded from the data bus by three separate write addresses
(<a href="https://alienbill.com/2600/101/docs/stella.html#PF">PF0</a>, PFl, PF2). Playfield may be loaded at any time. To clear the playfield,
zeros must be written into all three addresses.
<p>
</p></blockquote>
B. Normal Serial Output
<blockquote>
The playfield register is automatically scanned (and converted to serial
output) by a bi-directional shift register clocked at a rate which spreads the
twenty (20) bits out over the left half of a horizontal line. This scanning is
initiated by the end of horizontal blank (left edge of television screen).
Normally the same scan is then repeated, duplicating the same twenty (20)
bit sequence over the right half of the horizontal line.
<p>
</p></blockquote>
C. Reflected Serial Output
<blockquote>
A reflected playfield may be requested by writing a one into bit zero of the
playfield control register (<a href="https://alienbill.com/2600/101/docs/stella.html#CTRLPF">CTRLPF</a>). When this bit is true the scanning
shift register will scan the opposite direction during the right half of the
horizontal line, reversing the twenty (20) bit sequence.
<p>
</p></blockquote>
D. Timing Constraints
<blockquote>
Even though the playfield bytes (<a href="https://alienbill.com/2600/101/docs/stella.html#PF">PF0</a>, PFl, PF2) may be written to any time,
if one of them is changed while being serially scanned, part of the new value
may both show up on the television horizontal line.
<p>
</p></blockquote>
</blockquote>
<a name="tia1a4"></a>
4. Horizontal Position Counters
<blockquote>
<p>
A. Description
</p><blockquote>
The playfield is a fixed graphics register, always starting its serial output
when triggered by the beginning of each television line. This chip also
includes five "moveable" graphics registers, whose serial outputs are
triggered by five separate horizontal position counters every time these
counters pass through zero count. These position counters are clocked
continuously during the unblanked portion of every horizontal line and
their count length is exactly equal to the normal number of clocks supplied
to them during this time. They will therefore pass through zero at the same
time during each horizontal television line and the triggered outputs will
have no horizontal motion. A typical horizontal counter is shown in figure 4.
<p>
If extra clocks are supplied to these counters (or normal clocks suppressed)
the zero crossing time will shift and the object will have moved left (extra
clocks) or right (fewer clocks). Some position counters have extra decoders
(in addition to a zero decode) to trigger multiple copies of the same object
across a horizontal line.
</p><p>
All position counters can be reset to zero count by the microprocessor at any
time, by a write instruction to the reset addresses (<a href="https://alienbill.com/2600/101/docs/stella.html#RESBL">RESBL</a>, <a href="https://alienbill.com/2600/101/docs/stella.html#RESM">RESM0</a>, RESMl,
<a href="https://alienbill.com/2600/101/docs/stella.html#RESP">RESP0</a>, RESPl). If reset occurs during horizontal blank, the object will
appear at the left side of the television screen. Properly timed resets may
position an object at any horizontal location consistent with the
microprocessor cycle time.
</p><p>
</p></blockquote>
B. Ball position Counter
<blockquote>
The ball position counter has only the zero crossing decode and therefore
cannot trigger multiple copies of the ball graphics.
<p>
</p></blockquote>
C. Player Position Counters
<blockquote>
Each player position counter has three decodes in addition to the zero
crossing decode. These decodes are controlled by bits 0,1,2 of the number
size control registers (<a href="https://alienbill.com/2600/101/docs/stella.html#NUSIZ">NUSIZ0</a>, NUSIZ1), and trigger 1,2, or 3 copies of the
player (at various spacings) across a horizontal line as shown on page <a href="https://alienbill.com/2600/101/docs/stella.html#NUSIZ">___</a>.
These same control bits are used for the decodes on the missile position
counter, insuring an equal number of players and missiles.
</blockquote>
D. Missile Position Counters
<blockquote>
Missile position counters are identical to player position counters except
that they have another type of reset in addition to the previously discussed
horizontal position reset. These extra reset addresses (<a href="https://alienbill.com/2600/101/docs/stella.html#RESMP">RESMP0</a>, RESMP1)
write data bit 1 into a one bit register whose output is used to position the
missile (horizontally) directly on top of its corresponding player, and to
disable the missile serial output.
<p>
</p></blockquote>
</blockquote>
<a name="tia1a5"></a>
5. Horizontal Motion Registers
<p>
</p><blockquote>
A. General Description
<blockquote>
There are five write only registers on this chip that contain the horizontal
motion values for each of the five moving objects. A typical horizontal
motion register is shown in figure 4 . The data bus (bits 4 through 7) is
written into these addresses (<a href="https://alienbill.com/2600/101/docs/stella.html#HMP">HMP0</a>, HMPl, <a href="https://alienbill.com/2600/101/docs/stella.html#HMM">HMM0</a>, HMMl, <a href="https://alienbill.com/2600/101/docs/stella.html#HMBL">HMBL</a>) to load
these registers with motion values. These registers supply extra (or fewer)
clocks to the horizontal position counters only when commanded to do so by
an <a href="https://alienbill.com/2600/101/docs/stella.html#HMOVE">HMOVE</a> address from the microprocessor. These registers may all be
cleared to zero (no motion) simultaneously by an <a href="https://alienbill.com/2600/101/docs/stella.html#HMCLR">HMCLR</a> command from
the microprocessor, or individually by loading zeros into each register.
These registers are each four bits in length and may be loaded with positive
(left motion), negative (right motion) or zero (no motion) values. Negative
values are represented in twos complement format.
<p>
</p></blockquote>
B. Timing constraints
<blockquote>
These registers may be loaded or cleared at almost any time. The motion
values they contain will be used only when an HMOVE command is
addressed, and then all five motion values will be used simultaneously into
all five horizontal position counters once. The only timing constraint on this
operation involves the <a href="https://alienbill.com/2600/101/docs/stella.html#HMOVE">HMOVE</a> command. The HMOVE command must be
located in the microprocessor program immediately after a wait for sync
(WSYNC) command. This assures that the HMOVE operation begins at the
leading edge of horizontal blank, and has the full blank time to supply extra
or fewer clocks to the horizontal position counters. These registers should
not be modified for at least 24 Computer cycles after the HMOVE command.
<p>
</p></blockquote>
</blockquote>
<a name="tia1a6"></a>
6. Moving Object Graphics Registers
<p>
</p><blockquote>
A. General Description
<blockquote>
There are five graphics registers for moving objects on this chip. These
graphics registers are loaded (written) in parallel by the microprocessor and
like the playfield register are scanned and converted to serial output.
Unlike the playfield register, which is always scanned beginning at the left
side of each horizontal line, moving object graphics registers are scanned
only when triggered by a start decode from their horizontal position
counter. A typical graphics register is shown in figure 4 .
<p>
</p></blockquote>
B. Missile Graphics
<blockquote>
The graphics registers for both missiles are identical and very simple. They
each consist of a one bit register called missile enable (<a href="https://alienbill.com/2600/101/docs/stella.html#ENAM">ENAM0</a>, ENAM1).
This graphics bit is scanned (outputted) only when triggered by its
corresponding position counter. There are control bits (bits 4, 5, of <a href="https://alienbill.com/2600/101/docs/stella.html#NUSIZ">NUSIZ0</a>,
NUSIZ1) that can stretch this single graphics bit out over widths of 1, 2, 4,
or 8 clocks of horizontal line time. (A full line is 160 clocks).
<p>
</p></blockquote>
C. Player Graphics
<blockquote>
The graphics registers for both players are identical and are rather complex.
They each consist of eight bit parallel registers (<a href="https://alienbill.com/2600/101/docs/stella.html#GRP">GRP0</a>, GRP1) and a bi-
directional parallel to serial scan counter that converts the parallel data
into serial output. A one bit control register (<a href="https://alienbill.com/2600/101/docs/stella.html#REFP">REFP0</a>, REFP1) determines
the direction (reflection) of the parallel to serial scan, outputing either D7
through D0, or D0 though D7. This allows reflection (horizontal flipping) of
player serial graphics data without having to flip the microprocessor data.
<p>
The clock into the scan counter can be controlled (three bits of <a href="https://alienbill.com/2600/101/docs/stella.html#NUSIZ">NUSIZ0</a> and
NUSIZ1) to slow the scan rate and stretch the eight bits of serial graphics
out over widths of 8, 16, or 32 clocks of horizontal line time. These same
control bits are used in the player-missile motion counters to control
multiple copies, so only three player widths ( scan
rates) are available.
</p><p>
</p></blockquote>
D. Vertical Delay
<blockquote>
Each of the player graphics registers actually consists of two 8 bit parallel
registers. The first (<a href="https://alienbill.com/2600/101/docs/stella.html#GRP">GRP0</a>, GRP1) is loaded (written) from the
microprocessor 8 bit data bus. The second is automatically loaded from the
output of the first. The reason for this is a complex subject called vertical
delay. A large amount of microprocessor time is required to generate
player, missile and playfield graphics (table look up, masking, comparisons,
etc.) and load these into this chip's registers. For most game programs this
time is just too large to fit into one horizontal line time. In fact for most
games it will barely fit into two line times (127 microseconds). Therefore,
individual graphics registers are loaded (written) every two lines, and used
twice for serial output between loads. This type of programing will
obviously limit the vertical height resolution of objects to multiples of two
lines. It also will limit the resolution of vertical motion to two lines jumps.
Nothing can be done about the vertical height resolution; however, vertical
motion can be resolved to a single line by addition of a second graphics
register that is automatically parallel loaded from the output of the first,
one line time after the first was loaded from the data bus. This second
graphics register output is therefore always delayed vertically by one line. A
control bit called vertical delay (<a href="https://alienbill.com/2600/101/docs/stella.html#VDELP">VDEL0</a>, VDEL1) selects which of these two
registers is to be used for serial output. If this control bit is set by the
microprocessor between picture frames, the object will be moved down
(delayed) by one line during the next frame. In most programming
applications player 0 graphics and player 1 graphics are loaded (written)
alternately, during the blank time just prior to each line as shown in (figure
1). Since <a href="https://alienbill.com/2600/101/docs/stella.html#GRP">GRP0</a> and GRP1 addresses from the microprocessor alternate,
they are delayed by one line from each other. The GRP0 address decode can
therefore be used to load the delayed graphics register for player 1, and
GRP1 likewise to load the delayed graphics register for player 0. The two
vertical delay bits (<a href="https://alienbill.com/2600/101/docs/stella.html#VDELP">VDEL0</a>, VDELl) then select delayed or undelayed
registers for player 0 and player 1 as serial outputs.
<p>
</p></blockquote>
E. Ball Graphics
<blockquote>
The ball graphics register is almost identical to the missile graphics
register. It also consists of a single enable bit (<a href="https://alienbill.com/2600/101/docs/stella.html#ENABL">ENABL</a>) whose output is
triggered by the ball position counter. It also has two control bits (bits 4, 5
of <a href="https://alienbill.com/2600/101/docs/stella.html#CTRLPF">CTRLPF</a>) that can stretch this single graphics bit out over widths of 1, 2,
4, or 8 clocks of horizontal line time. Unlike the missile graphics; however,
the ball graphics register has capability for vertical delay similar to the
player graphics. A second graphics (enable) bit is alternately loaded from
the output of the first, one line after the first was loaded from the data bus.
A ball vertical delay bit (<a href="https://alienbill.com/2600/101/docs/stella.html#VDELBL">VDELBL</a>) selects which of these two graphics bits
is used for the ball serial output. The first graphics bit (ENABL) should be
loaded during the same horizontal blank time as player 0 (<a href="https://alienbill.com/2600/101/docs/stella.html#GRP">GRP0</a>), because
GRP1 is used to load the second enable bit from the output of the first on
alternate lines.
<p>
</p></blockquote>
</blockquote>
<a name="tia1a7"></a>
7. Collision Detection Latches
<p>
</p><blockquote>
A. Definitions
<blockquote>
The serial outputs from all the graphics registers represent real time
horizontal location of objects on the television screen. If any of these outputs
occur at the same time, they will overlap (collide) on the screen. There are
six objects generated on this chip (five moving and playfield) allowing
fifteen possible two object collisions. These overlaps (collisions) are detected
by fifteen "and" gates whenever they occur, and are stored in fifteen
individual latch register bits, as shown in figure 6.
<p>
</p></blockquote>
B. Reading Collision
<blockquote>
The microprocessor can read these fifteen collision bits on data lines 6 and 7
by addressing them two at a time. This could be done at any time but is
usually done between frames (during vertical blank) after all possible
collisions have serially occurred.
<p>
</p></blockquote>
C. Reset
<blockquote>
All collision bits are reset simultaneously by the microprocessor using the
reset address <a href="https://alienbill.com/2600/101/docs/stella.html#CXCLR">CXCLR</a>. This is usually done near the end of vertical blank,
after collisions have been tested.
<p>
</p></blockquote>
</blockquote>
<p>
<a name="tia1a8"></a>
8. Input ports
</p><p>
</p><blockquote>
A. General Description
<blockquote>
There are 6 input ports on this chip whose logic state may be read on data
line 7 with read addresses <a href="https://alienbill.com/2600/101/docs/stella.html#INPT">INPT0</a> through INPT5. These 6 ports are
divided into two types, "dumped" and "latched". See Figure 8.
<p>
</p></blockquote>
B. Dumped Input Ports (I0 through I3)
<blockquote>
These 4 input ports are normally used to read paddle position from an
external potentiometer-capacitor circuit. In order to discharge these
capacitors each of these input ports has a large transistor, which may be
turned on (grounding the input ports) by writing into bit 7 of the register
<a href="https://alienbill.com/2600/101/docs/stella.html#VBLANK">VBLANK</a>. When this control bit is cleared the potentiometers begin to
recharge the capacitors and the microprocessor measures the time required
to detect a logic 1 at each input port.
<p>
As long as bit 7 of register VBLANK is zero, these four ports are general
purpose high impedance input ports. When this bit is a 1 these ports are
grounded.
</p><p>
</p></blockquote>
C. Latched Input ports (I4, I5)
<blockquote>
These two input ports have latches which can be enabled or disabled by
writing into bit 6 of register VBLANK.
<p>
When disabled, these latches are removed from the circuit completely and
these ports become two general purpose input ports, whose present logic
state can be read directly by the microprocessor.
</p><p>
When enabled, these latches will store negative (zero logic level) signals
appearing on these two input ports, and the input port addresses will read
the latches instead of the input ports.
</p><p>
When first enabled these latches will remain positive as long as the input
ports remain positive (logic one). A zero input port signal will clear a latch
value to zero, where it will remain (even after the port returns positive)
until disabled. Both latches may be simultaneously disabled by writing a
zero into bit 6 of register <a href="https://alienbill.com/2600/101/docs/stella.html#VBLANK">VBLANK</a>.
</p><p>
</p></blockquote>
</blockquote>
<a name="tia1a8.5"></a>
8.5 Priority Encoder
<p>
</p><blockquote>
A. Purpose
<blockquote>
As discussed in the section on collisions, simultaneous serial outputs from
the graphics registers represent overlap on the television screen. In order to
have color-luminosity values assigned to individual objects it is necessary to
establish priorities between objects when overlapped. The priority encoder
is shown in figure 3.
<p>
</p></blockquote>
B. Priority Assignment
<blockquote>
The lack of any objects results in a color-lum value called the background.
The background (BK) has lowest priority and only appears when no objects
are outputing. In order to simplify the logic, each missile is given the same
color-lum value and priority as its corresponding player (P0, M0) and the
ball is given the same color-lum value and priority as the playfield (PF, BL).
<p>
The following table illustrates the normal priority assignment:
</p><p>
</p><blockquote>
<table border="1">
<tbody><tr><td>Highest Priority</td><td> P0, M0</td></tr>
<tr><td>Second Highest</td><td> P1, M1</td></tr>
<tr><td>Third Highest</td><td> PF, BL</td></tr>
<tr><td>Lowest Priority</td><td> BK</td></tr>
</tbody></table>
</blockquote>
<p>
Objects with higher priority will appear to move in front of objects with
lower priority. Players will therefore move in front of playfield (clouds,
walls, etc.).
</p><p>
</p></blockquote>
C. Priority Control
<blockquote>
There are two playfield control bits that affect priority, one called playfield
priority (PFP) (bit 2 of <a href="https://alienbill.com/2600/101/docs/stella.html#CTRLPF">CTRLPF</a>) and one called score (bit 1 of CTRLPF).
When a one is written into the PFP bit the priority assignment is modified
as shown below.
<p>
</p><blockquote>
<table border="1">
<tbody><tr><td>Highest Priority</td><td> PF, BL</td></tr>
<tr><td>Second Highest</td><td> P0, M0</td></tr>
<tr><td>Third Highest</td><td> P1, M1</td></tr>
<tr><td>Lowest Priority</td><td> BK</td></tr>
</tbody></table>
</blockquote>
<p>
Players will then move behind playfield (clouds, wall, etc.). When a one is
written into the score control bit, the playfield is forced to take the color-lum
of player 0 in the left half of the screen and player 1 in the right half of the
screen. This is used when displaying score and identifies the score with the
correct player. The priority encoder produces 4 register select lines shown
in figure 3) that are mutually exclusive. These 4 lines select either
background, player 0, player 1 or playfield, and only one of them can be
true at a time.
</p><p>
</p></blockquote>
</blockquote>
<a name="tia1a9"></a>
9. Color Luminance Registers
<p>
</p><blockquote>
A. Description
<blockquote>
There are four registers (shown in figure 3) that contain color-lum codes.
Four bits of color code and three its of luminance code may be written into
each of these registers (<a href="https://alienbill.com/2600/101/docs/stella.html#COLUP">COLUP0</a>, COLUP1, COLUPF, COLUBK) by the
microprocessor at any time. These codes (representing 16 color values and 8
luminance values) are given in the Detailed Address List.
<p>
</p></blockquote>
B. Multiplexing
<blockquote>
The serial graphics output from all six objects is examined by the priority
encoder which activates one of the four select lines into a 4 x 7 multiplexer.
This multiplexer (shown in figure 3) then selects one of the four color-lum
registers as a 7 line output. Three of these lines are binary coded
luminosity and go directly to chip output pads. The other four lines go to the
color phase shifter.
<p>
</p></blockquote>
</blockquote>
<a name="tia1a10"></a>
10. Color Phase Shifter
<p>
</p><blockquote>
This portion of the chip (shown in figure 3) produces a reference color
output (color burst) during horizontal blank and then during the unblanked
portion of the line it produces a color output shifted in phase with respect to
the color burst. The amount of phase shift determines the color and is
selected by the four color code lines from the Color-lum multiplexer. Binary
code 0 selects no color. Code 1 selects gold (same phase as color burst).
Codes 2 (0010) through 15 (1111) shift the phase from zero through almost
360 degrees allowing selection of 15 total colors around the television color
wheel.
<p>
</p></blockquote>
<a name="tia1a11"></a>
11. Audio Circuits
<p>
</p><blockquote>
Two audio circuits are incorporated on this chip. They are identical and
completely independent, although their outputs could be combined
externally into one speaker. Each audio circuit consists of parts described
below, and in figure 7.
<p>
A. Frequency Select
</p><blockquote>
Clock pulses (at approximately 30 KHz) from the horizontal sync counter
pass through a divide by N circuit which is controlled by the output code
from a five bit frequency register (<a href="https://alienbill.com/2600/101/docs/stella.html#AUDF">AUDF</a>). This register can be loaded
(written) by the microprocessor at any time, and causes the 30 KHz clocks
to be divided by 1 (code 00000) through 32 (code 11111). This produces
pulses that are digitally adjustable from approximately 30 KHz to 1 KHz
and are used to clock the noise-tone generator.
</blockquote>
B. Noise-Tone Generator
<blockquote>
This circuit contains a nine bit shift counter which may be controlled by the
output code from a four bit audio control register(<a href="https://alienbill.com/2600/101/docs/stella.html#AUDC">AUDC</a>), and is clocked by
the frequency select circuit. The control register can be loaded by the
microprocessor at any time, and selects different shift counter feedback taps
and count lengths to produce a variety of noise and tone qualities.
<p>
</p></blockquote>
C. Volume Select
<blockquote>
The shift counter output is used to drive the audio output pad through four
driver transistors that are graduated in size. Each transistor is twice as
large as the previous one and is enable by one bit from the audio volume
register (<a href="https://alienbill.com/2600/101/docs/stella.html#AUDV">AUDV</a>). This audio volume register may be loaded by the
microprocessor at any time. As binary codes 0 through 15 are loaded, the
pad drive transistors are enabled in a binary sequence. The shift counter
output therefore can pull down on the audio output pad with 16 selectable
impedance levels.
</blockquote>
</blockquote>
<p>
</p><hr>
<p>
<a href="https://alienbill.com/2600/101/docs/figure1.gif">Figure 1. Vertical Delay</a></p><p>
<a href="https://alienbill.com/2600/101/docs/figure2.gif">Figure 2. Synchronization<br>Figure 3. Color-Luminance</a></p><p>
<a href="https://alienbill.com/2600/101/docs/figure4.gif">Figure 4. Typical Horizontal Motion Circuit</a></p><p>
<a href="https://alienbill.com/2600/101/docs/figure5.gif">Figure 5. Playfield Graphics</a></p><p>
<a href="https://alienbill.com/2600/101/docs/figure6.gif">Figure 6. Collision Detection</a></p><p>
<a href="https://alienbill.com/2600/101/docs/figure7.gif">Figure 7. Audio Circuit</a></p><p>
<a href="https://alienbill.com/2600/101/docs/figure8.gif">Figure 8. Input Ports</a></p><p>
<a href="https://alienbill.com/2600/101/docs/figure9.gif">Figure 9. Game System</a></p><p>
</p><p>
</p><hr>
<p>
<a name="W"></a>
</p><h3>Write Address Detailed Functions</h3>
<p>
<a name="WSYNC"></a>
WSYNC (wait for sync)
</p><blockquote>
This address halts microprocessor by clearing RDY latch to zero. RDY is set true again
by the leading edge of horizontal blank.
<p>
Data bits not used
</p></blockquote>
<a name="RSYNC"></a>
RSYNC (reset sync)
<blockquote>
This address resets the horizontal sync counter to define the beginning of horizontal
blank time, and is used in chip testing.
<p>
Data bits not used.
</p></blockquote>
<a name="VSYNC"></a>
VSYNC
<blockquote>
This address controls vertical sync time by writing D1 into the VSYNC latch
<blockquote>
<table border="1">
<tbody><tr><td colspan="2">D1</td></tr>
<tr><td>0</td><td>Stop vertical sync</td></tr>
<tr><td>1</td><td>Start vertical sync</td></tr>
</tbody></table>
</blockquote>
</blockquote>
<a name="VBLANK"></a>
VBLANK
<blockquote>
This address controls vertical blank and the latches and dumping transistors on the input
ports by writing into bits D7, D6 and D1 of the VBLANK register.
<blockquote>
<table border="1">
<tbody><tr><td>Data Bit</td><td>Value</td><td>Effect</td></tr>
<tr><td rowspan="2">D1</td><td>0</td><td>Stop vert. blank</td></tr>
<tr><td>1</td><td>Start vert. blank</td></tr>
<tr><td rowspan="2">D6</td><td>0</td><td>Disable INPT4, INPT5 latches</td></tr>
<tr><td>1</td><td>Enable INPT4, INPT5 latches</td></tr>
<tr><td rowspan="2">D7</td><td>0</td><td>Remove INPT1,2,3,6 dump path to ground</td></tr>
<tr><td>1</td><td>Dump INPT1,2,3,6 to ground</td></tr>
</tbody></table>
Note : Disable latches (D6 = 0) also resets latches to logic true
</blockquote>
</blockquote>
<a name="PJ"></a>
PF0 (PF1, PF2)
<blockquote>
These addresses are used to write into playfield registers
<blockquote>
<table border="1">
<tbody><tr><td>PF0</td><td>D7</td><td>D6</td><td>D5</td><td>D4</td><td colspan="4">(not used)</td></tr>
<tr><td>PF1</td><td>D7</td><td>D6</td><td>D5</td><td>D4</td><td>D3</td><td>D2</td><td>D1</td><td>D0</td></tr>
<tr><td>PF2</td><td>D7</td><td>D6</td><td>D5</td><td>D4</td><td>D3</td><td>D2</td><td>D1</td><td>D0</td></tr>
</tbody></table>
</blockquote>
</blockquote>
<a name="PLAYFIELD"></a>
PLAYFIELD REGISTERS SERIAL OUTPUT
<blockquote>
<table border="1">
<tbody><tr><td colspan="6">1 horizontal line ( 160 clocks)</td><td>Playfield Reflect Control</td></tr>
<tr><td>4..7</td><td> 7......0</td><td> 0......7</td><td> 4..7</td><td> 7......0</td><td> 0......7</td><td rowspan="3"> REF = 0</td></tr>
<tr><td>PF0</td><td>PF1</td><td>PF2</td><td>PF0</td><td>PF1</td><td>PF2</td></tr>
<tr><td colspan="6" align="center">center</td></tr>
</tbody></table>
<table border="1">
<tbody><tr><td>4..7</td><td> 7......0</td><td> 0......7</td><td> 7......0</td><td> 0......7</td><td> 7..4</td><td rowspan="2"> REF = 1</td></tr>
<tr><td>PF0</td><td> PF1</td><td> PF2</td><td> PF2</td><td> PF1</td><td> PF0</td></tr>
</tbody></table>
<p>
each bit = 4 clocks
</p></blockquote>
<a name="CTRLPF"></a>
CTRLPF
<blockquote>
This address is used to write into the playfield control register
(a logic 1 causes action as described below)
<blockquote>
<table border="1">
<tbody><tr><td>D0</td><td>REF (reflect playfield)</td></tr>
<tr><td>D1</td><td>SCORE (left half of playfield gets color of player 0, right half gets color of player</td></tr>
<tr><td>D2</td><td>PFP (playfield gets priority over players so they can move behind the playfield)</td></tr>
<tr><td>D4</td><td rowspan="2">Ball Size (see next table)</td></tr>
<tr><td>D5</td></tr>
</tbody></table>
<p>
D4 &amp; D5 = BALL SIZE
<table border="1">
<tbody><tr><td>D5</td><td>D4</td><td>Width</td></tr>
<tr><td>0</td><td>0</td><td>1 clock</td></tr>
<tr><td>0</td><td>1</td><td>2 clocks</td></tr>
<tr><td>1</td><td>0</td><td>4 clocks</td></tr>
<tr><td>1</td><td>1</td><td>8 clocks</td></tr>
</tbody></table>
</p></blockquote>
</blockquote>
<a name="NUSIZ"></a>
NUSIZ0 (NUSIZ1)
<blockquote>
These addresses control the number and size of players and missiles.
<blockquote>
Missile Size
<table border="1">
<tbody><tr><td>D5</td><td>D4</td><td>Width</td></tr>
<tr><td>0</td><td>0</td><td>1 clock</td></tr>
<tr><td>0</td><td>1</td><td>2 clocks</td></tr>
<tr><td>1</td><td>0</td><td>4 clocks</td></tr>
<tr><td>1</td><td>1</td><td>8 clocks</td></tr>
</tbody></table>
<p>
Player-Missile number &amp; player size
<table border="1">
<tbody><tr><td>D2</td><td>D1</td><td>D0</td><td colspan="9">1/2 television line (80 clocks)<br>8 clocks per square</td><td>Description</td></tr>
<tr><td>0</td><td>0</td><td>0</td>
<td width="20">X</td>
<td width="20">&nbsp;</td>
<td width="20">&nbsp;</td>
<td width="20">&nbsp;</td>
<td width="20">&nbsp;</td>
<td width="20">&nbsp;</td>
<td width="20">&nbsp;</td>
<td width="20">&nbsp;</td>
<td width="20">&nbsp;</td>
<td>one copy</td></tr>
<tr><td>0</td><td>0</td><td>1</td>
<td width="20">X</td>
<td width="20">&nbsp;</td>
<td width="20">X</td>
<td width="20">&nbsp;</td>
<td width="20">&nbsp;</td>
<td width="20">&nbsp;</td>
<td width="20">&nbsp;</td>
<td width="20">&nbsp;</td>
<td width="20">&nbsp;</td>
<td>two copies - close</td></tr>
<tr><td>0</td><td>1</td><td>0</td>
<td>X</td>
<td width="20">&nbsp;</td>
<td width="20">&nbsp;</td>
<td width="20">&nbsp;</td>
<td width="20">X</td>
<td width="20">&nbsp;</td>
<td width="20">&nbsp;</td>
<td width="20">&nbsp;</td>
<td width="20">&nbsp;</td>
<td>two copies - med</td></tr>
<tr><td>0</td><td>1</td><td>1</td>
<td width="20">X</td>
<td width="20">&nbsp;</td>
<td width="20">X</td>
<td width="20">&nbsp;</td>
<td width="20">X</td>
<td width="20">&nbsp;</td>
<td width="20">&nbsp;</td>
<td width="20">&nbsp;</td>
<td width="20">&nbsp;</td>
<td>three copies - close</td></tr>
<tr><td>1</td><td>0</td><td>0</td>
<td width="20">X</td>
<td width="20">&nbsp;</td>
<td width="20">&nbsp;</td>
<td width="20">&nbsp;</td>
<td width="20">&nbsp;</td>
<td width="20">&nbsp;</td>
<td width="20">&nbsp;</td>
<td width="20">&nbsp;</td>
<td width="20">X</td>
<td>two copies - wide</td></tr>
<tr><td>1</td><td>0</td><td>1</td>
<td width="20">X</td>
<td width="20">X</td>
<td width="20">&nbsp;</td>
<td width="20">&nbsp;</td>
<td width="20">&nbsp;</td>
<td width="20">&nbsp;</td>
<td width="20">&nbsp;</td>
<td width="20">&nbsp;</td>
<td width="20">&nbsp;</td>
<td width="20">double size player</td></tr>
<tr><td>1</td><td>1</td><td>0</td>
<td width="20">X</td>
<td width="20">&nbsp;</td>
<td width="20">&nbsp;</td>
<td width="20">&nbsp;</td>
<td width="20">X</td>
<td width="20">&nbsp;</td>
<td width="20">&nbsp;</td>
<td width="20">&nbsp;</td>
<td width="20">X</td>
<td>3 copies medium</td></tr>
<tr><td>1</td><td>1</td><td>1</td>
<td width="20">X</td>
<td width="20">X</td>
<td width="20">X</td>
<td width="20">X</td>
<td width="20">&nbsp;</td>
<td width="20">&nbsp;</td>
<td width="20">&nbsp;</td>
<td width="20">&nbsp;</td>
<td width="20">&nbsp;</td>
<td>quad sized player</td></tr>
</tbody></table>
</p></blockquote>
</blockquote>
<a name="RESP"></a>
<a name="RESM"></a>
<a name="RESBL"></a>
RESP0 (RESP1, RESM0, RESM1, RESBL)
<blockquote>
These addresses are used to reset players, missiles and the ball. The object will begin its
serial graphics at the time of a horizontal line at which the reset address occurs.
<p>
No data bits are used
</p></blockquote>
<a name="RESMP"></a>
RESMP0 (RESMP1)
<blockquote>
These addresses are used to reset the horiz. location of a missile to the center of its
corresponding player. As long as this control bit is true (1) the missile will remain
locked to the center of its player and the missile graphics will be disabled. When a
zero is written into this location, the missile is enabled, and can be moved independently
from the player.
<p>
</p><blockquote>
D1 = RESMP (missile-player reset)
</blockquote>
</blockquote>
<a name="HMOVE"></a>
HMOVE
<blockquote>
This address causes the horizontal motion register values to be acted upon during the
horizontal blank time in which it occurs. It must occur at the beginning of horiz. blank in
order to allow time for generation of extra clock pulses into the horizontal position
counters if motion is desired this command must immediately follow a WSYNC
command in the program.
<p>
No data bits are used.
</p></blockquote>
<a name="HMCLR"></a>
HMCLR
<blockquote>
This address clears all horizontal motion registers to zero (no motion).
No data bits are used.
</blockquote>
<a name="HMP"></a>
<a name="HMM"></a>
<a name="HMBL"></a>
HMP0 (HMP1, HMM0, HMM1, HMBL)
<blockquote>
These addresses write data (horizontal motion values) into the horizontal motion
registers. These registers will cause horizontal motion only when commanded to do so
by the horiz. move command HMOVE.
The motion values are coded as shown below :
<blockquote>
<table border="1">
<tbody><tr><td>D7</td><td>D6</td><td>D5</td><td>D4</td><td>Clocks</td><td>Effect</td></tr>
<tr><td>0</td><td>1</td><td>1</td><td>1</td><td>+7</td><td rowspan="7">Move left indicated number of clocks</td></tr>
<tr><td>0</td><td>1</td><td>1</td><td>0</td><td>+6</td></tr>
<tr><td>0</td><td>1</td><td>0</td><td>1</td><td>+5</td></tr>
<tr><td>0</td><td>1</td><td>0</td><td>0</td><td>+4</td></tr>
<tr><td>0</td><td>0</td><td>1</td><td>1</td><td>+3</td></tr>
<tr><td>0</td><td>0</td><td>1</td><td>0</td><td>+2</td></tr>
<tr><td>0</td><td>0</td><td>0</td><td>1</td><td>+1</td></tr>
<tr><td>0</td><td>0</td><td>0</td><td>0</td><td>0</td><td>No Motion</td></tr>
<tr><td>1</td><td>1</td><td>1</td><td>1</td><td>-1</td><td rowspan="8">Move right indicated number of clocks</td></tr>
<tr><td>1</td><td>1</td><td>1</td><td>0</td><td>-2</td></tr>
<tr><td>1</td><td>1</td><td>0</td><td>1</td><td>-3</td></tr>
<tr><td>1</td><td>1</td><td>0</td><td>0</td><td>-4</td></tr>
<tr><td>1</td><td>0</td><td>1</td><td>1</td><td>-5</td></tr>
<tr><td>1</td><td>0</td><td>1</td><td>0</td><td>-6</td></tr>
<tr><td>1</td><td>0</td><td>0</td><td>1</td><td>-7</td></tr>
<tr><td>1</td><td>0</td><td>0</td><td>0</td><td>-8</td></tr>
</tbody></table>
</blockquote>
WARNING : These motion registers should not be modified during the 24 computer
cycles immediately following an HMOVE command. Unpredictable motion values may
result.
</blockquote>
<a name="ENAM"></a>
<a name="ENABL"></a>
ENAM0 (ENAM1, ENABL)
<blockquote>
These addresses write D1 into the 1 bit missile or ball graphics registers.
<blockquote>
<table border="1">
<tbody><tr><td colspan="2">D1</td></tr>
<tr><td>0</td><td>Disables object</td></tr>
<tr><td>1</td><td>Enables object</td></tr>
</tbody></table>
</blockquote>
</blockquote>
<a name="GRP"></a>
GRP0 (GRP1)
<blockquote>
These addresses write data into the player graphics registers.
<blockquote>
<table border="1">
<tbody><tr><td>D7</td><td>D6</td><td>D5</td><td>D4</td><td>D3</td><td>D2</td><td>D1</td><td>D0</td></tr>
<tr><td colspan="8">Graphics Data</td></tr>
</tbody></table>
</blockquote>
Note: serial output begins with D7, unless REFP0 (REFP1) = 1
</blockquote>
<a name="REFP"></a>
REFP0 (REFP1)
<blockquote>
These addesses write D3 into the 1 bit player reflect registers
<blockquote>
<table border="1">
<tbody><tr><td colspan="2">D3</td></tr>
<tr><td>0</td><td>no reflect, D7 of GRPx on left</td></tr>
<tr><td>1</td><td>reflect, D0 of GRPx on left</td></tr>
</tbody></table>
</blockquote>
</blockquote>
<a name="VDELP"></a>
<a name="VDELBL"></a>
VDELP0 (VDELP1, VDELBL)
<blockquote>
These addresses write D0 into the 1 bit vertical delay registers, to delay players or ball by
one vertical line.<p>
</p><blockquote>
<table border="1">
<tbody><tr><td colspan="2">D0</td></tr>
<tr><td>0</td><td>no delay</td></tr>
<tr><td>1</td><td>delay</td></tr>
</tbody></table>
</blockquote>
</blockquote>
<a name="CXCLR"></a>
CXCLR
<blockquote>
This adderess clears all collision latches to zero (no collision).
No data bits are used.
</blockquote>
<a name="COLUP"></a>
COLUP0 (COLUP1, COLUPF, COLUBK)
<blockquote>
These addresses write data into the player, playfield, and background color-luminance
registers
<p>
</p><blockquote>
<table border="1">
<tbody><tr><td>COLOR</td><td>D7</td><td>D6</td><td>D5</td><td>D4</td><td>D3</td><td>D2</td><td>D1</td><td>LUM</td></tr>
<tr><td>grey - gold</td><td>0</td><td>0</td><td>0</td><td>0</td><td>0</td><td>0</td><td>0</td><td>black</td></tr>
<tr><td>&nbsp;</td><td>0</td><td>0</td><td>0</td><td>1</td><td>0</td><td>0</td><td>1</td><td>dark grey</td></tr>
<tr><td>orange, brt-org</td><td>0</td><td>0</td><td>1</td><td>0</td><td>0</td><td>1</td><td>0</td></tr>
<tr><td>&nbsp;</td><td>0</td><td>0</td><td>1</td><td>1</td><td>0</td><td>1</td><td>1</td><td>grey</td></tr>
<tr><td>pink - purple</td><td>0</td><td>1</td><td>0</td><td>0</td><td>1</td><td>0</td><td>0</td></tr>
<tr><td>&nbsp;</td><td>0</td><td>1</td><td>0</td><td>1</td><td>1</td><td>0</td><td>1</td></tr>
<tr><td>purp-blue, blue</td><td>0</td><td>1</td><td>1</td><td>0</td><td>1</td><td>1</td><td>0</td><td>light grey</td></tr>
<tr><td>&nbsp;</td><td>0</td><td>1</td><td>1</td><td>1</td><td>1</td><td>1</td><td>1</td><td>white</td></tr>
<tr><td>blue - lt. blue</td><td>1</td><td>0</td><td>0</td><td>0</td></tr>
<tr><td>&nbsp;</td><td>1</td><td>0</td><td>0</td><td>1</td></tr>
<tr><td>torq. - grn. blue</td><td>1</td><td>0</td><td>1</td><td>0</td></tr>
<tr><td>&nbsp;</td><td>1</td><td>0</td><td>1</td><td>1</td></tr>
<tr><td>grn. - yel. grn.</td><td>1</td><td>1</td><td>0</td><td>0</td></tr>
<tr><td>&nbsp;</td><td>1</td><td>1</td><td>0</td><td>1</td></tr>
<tr><td>org. grn - lt org.</td><td>1</td><td>1</td><td>1</td><td>0</td></tr>
<tr><td>&nbsp;</td><td>1</td><td>1</td><td>1</td><td>1</td></tr>
</tbody></table>
</blockquote>
</blockquote>
<a name="AUDF"></a>
AUDF0 (AUDF1)
<blockquote>
These addresses write data into the audio frequency divider registers.
<p>
</p><blockquote>
<table border="1">
<tbody><tr><td>D4</td><td> D3</td><td> D2</td><td> D1</td><td> D0</td><td> 30KHz divided by</td></tr>
<tr><td>0</td><td>0</td><td>0</td><td>0</td><td>0</td><td>no division</td></tr>
<tr><td>0</td><td>0</td><td>0</td><td>0</td><td>1</td><td>divide by 2</td></tr>
<tr><td>0</td><td>0</td><td>0</td><td>1</td><td>0</td><td>divide by 3</td></tr>
<tr><td>...</td><td>...</td><td>...</td><td>...</td><td>...</td><td>...</td></tr>
<tr><td>1</td><td>1</td><td>1</td><td>1</td><td>0</td><td>divide by 31</td></tr>
<tr><td>1</td><td>1</td><td>1</td><td>1</td><td>1</td><td>divide by 32</td></tr>
</tbody></table>
</blockquote>
</blockquote>
<a name="AUDC"></a>
AUDC0 (AUDC1)
<blockquote>
These addresses write data into the audio control registers which control the noise
content and additional division of the audio output.
<p>
</p><blockquote>
<table border="1">
<tbody><tr><td>D3</td><td> D2</td><td> D1</td><td> D0</td><td> Type of noise or division</td></tr>
<tr><td>0</td><td>0</td><td>0</td><td>0</td><td>set to 1</td></tr>
<tr><td>0</td><td>0</td><td>0</td><td>1</td><td>4 bit poly</td></tr>
<tr><td>0</td><td>0</td><td>1</td><td>0</td><td>div 15 -&gt; 4 bit poly</td></tr>
<tr><td>0</td><td>0</td><td>1</td><td>1</td><td>5 bit poly -&gt; 4 bit poly</td></tr>
<tr><td>0</td><td>1</td><td>0</td><td>0</td><td>div 2 : pure tone</td></tr>
<tr><td>0</td><td>1</td><td>0</td><td>1</td><td>div 2 : pure tone</td></tr>
<tr><td>0</td><td>1</td><td>1</td><td>0</td><td>div 31 : pure tone</td></tr>
<tr><td>0</td><td>1</td><td>1</td><td>1</td><td>5 bit poly -&gt; div 2</td></tr>
<tr><td>1</td><td>0</td><td>0</td><td>0</td><td>9 bit poly (white noise)</td></tr>
<tr><td>1</td><td>0</td><td>0</td><td>1</td><td>5 bit poly</td></tr>
<tr><td>1</td><td>0</td><td>1</td><td>0</td><td>div 31 : pure tone</td></tr>
<tr><td>1</td><td>0</td><td>1</td><td>1</td><td>set last 4 bits to 1</td></tr>
<tr><td>1</td><td>1</td><td>0</td><td>0</td><td>div 6 : pure tone</td></tr>
<tr><td>1</td><td>1</td><td>0</td><td>1</td><td>div 6 : pure tone</td></tr>
<tr><td>1</td><td>1</td><td>1</td><td>0</td><td>div 93 : pure tone</td></tr>
<tr><td>1</td><td>1</td><td>1</td><td>1</td><td>5 bit poly div 6</td></tr>
</tbody></table>
</blockquote>
</blockquote>
<a name="AUDV"></a>
AUDV0 (AUDV1)
<blockquote>
These addresses write data into the audio volume registers which set the pull down
impedance driving the audio output pads.
<p>
</p><blockquote>
<table border="1">
<tbody><tr><td>D3</td><td> D2</td><td> D1</td><td> D0</td><td> Audio Output Pull down current</td></tr>
<tr><td>0</td><td> 0</td><td> 0</td><td> 0</td><td> No output current</td></tr>
<tr><td>0</td><td> 0</td><td> 0</td><td> 1</td><td> lowest</td></tr>
<tr><td>0</td><td> 0</td><td> 1</td><td> 0</td></tr>
<tr><td>...</td><td> ...</td><td> ...</td><td> ...</td></tr>
<tr><td>1</td><td> 1</td><td> 1</td><td> 0</td></tr>
<tr><td>1</td><td> 1</td><td> 1</td><td> 1</td><td> highest</td></tr>
</tbody></table>
</blockquote>
</blockquote>
<p>
</p><hr>
<p>
<a name="wsummary"></a>
</p><h3>TIA WRITE ADDRESS SUMMARY</h3>
<blockquote>
<table border="1">
<tbody><tr><td>6-bit Address</td><td>Address Name</td><td>7</td><td>6</td><td>5</td><td>4</td><td>3</td><td>2</td><td>1</td><td>0</td><td>Function</td></tr>
<tr><td>00</td><td><a href="https://alienbill.com/2600/101/docs/stella.html#VSYNC">VSYNC</a> </td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td>1</td><td>.</td><td> vertical sync set-clear</td></tr>
<tr><td>01</td><td><a href="https://alienbill.com/2600/101/docs/stella.html#VBLANK">VBLANK</a> </td><td>1</td><td>1</td><td>.</td><td>.</td><td>.</td><td>.</td><td>1</td><td>.</td><td> vertical blank set-clear</td></tr>
<tr><td>02</td><td><a href="https://alienbill.com/2600/101/docs/stella.html#WSYNC">WSYNC</a> </td><td colspan="8" align="center">strobe</td><td> wait for leading edge of horizontal blank</td></tr>
<tr><td>03</td><td><a href="https://alienbill.com/2600/101/docs/stella.html#RSYNC">RSYNC</a> </td><td colspan="8" align="center">strobe</td><td> reset horizontal sync counter</td></tr>
<tr><td>04</td><td><a href="https://alienbill.com/2600/101/docs/stella.html#NUSIZ">NUSIZ0</a> </td><td>.</td><td>.</td><td>1</td><td>1</td><td>1</td><td>1</td><td>1</td><td>1</td><td> number-size player-missile 0</td></tr>
<tr><td>05</td><td><a href="https://alienbill.com/2600/101/docs/stella.html#NUSIZ">NUSIZ1</a> </td><td>.</td><td>.</td><td>1</td><td>1</td><td>1</td><td>1</td><td>1</td><td>1</td><td> number-size player-missile 1</td></tr>
<tr><td>06</td><td><a href="https://alienbill.com/2600/101/docs/stella.html#COLUP">COLUP0</a> </td><td>1</td><td>1</td><td>1</td><td>1</td><td>1</td><td>1</td><td>1</td><td>.</td><td> color-lum player 0</td></tr>
<tr><td>07</td><td><a href="https://alienbill.com/2600/101/docs/stella.html#COLUP">COLUP1</a> </td><td>1</td><td>1</td><td>1</td><td>1</td><td>1</td><td>1</td><td>1</td><td>.</td><td> color-lum player 1</td></tr>
<tr><td>08</td><td><a href="https://alienbill.com/2600/101/docs/stella.html#COLUP">COLUPF</a> </td><td>1</td><td>1</td><td>1</td><td>1</td><td>1</td><td>1</td><td>1</td><td>.</td><td> color-lum playfield</td></tr>
<tr><td>09</td><td><a href="https://alienbill.com/2600/101/docs/stella.html#COLUP">COLUBK</a> </td><td>1</td><td>1</td><td>1</td><td>1</td><td>1</td><td>1</td><td>1</td><td>.</td><td> color-lum background</td></tr>
<tr><td>0A</td><td><a href="https://alienbill.com/2600/101/docs/stella.html#CTRLPF">CTRLPF</a> </td><td>.</td><td>.</td><td>1</td><td>1</td><td>.</td><td>1</td><td>1</td><td>1</td><td> control playfield ball size &amp; collisions</td></tr>
<tr><td>0B</td><td><a href="https://alienbill.com/2600/101/docs/stella.html#REFP">REFP0</a> </td><td>.</td><td>.</td><td>.</td><td>.</td><td>1</td><td>.</td><td>.</td><td>.</td><td> reflect player 0</td></tr>
<tr><td>0C</td><td><a href="https://alienbill.com/2600/101/docs/stella.html#REFP">REFP1</a> </td><td>.</td><td>.</td><td>.</td><td>.</td><td>1</td><td>.</td><td>.</td><td>.</td><td> reflect player 1</td></tr>
<tr><td>0D</td><td><a href="https://alienbill.com/2600/101/docs/stella.html#PF">PF0</a> </td><td>1</td><td>1</td><td>1</td><td>1</td><td>.</td><td>.</td><td>.</td><td>.</td><td> playfield register byte 0</td></tr>
<tr><td>0E</td><td><a href="https://alienbill.com/2600/101/docs/stella.html#PF">PF1</a> </td><td>1</td><td>1</td><td>1</td><td>1</td><td>1</td><td>1</td><td>1</td><td>1</td><td> playfield register byte 1</td></tr>
<tr><td>0F</td><td><a href="https://alienbill.com/2600/101/docs/stella.html#PF">PF2</a> </td><td>1</td><td>1</td><td>1</td><td>1</td><td>1</td><td>1</td><td>1</td><td>1</td><td> playfield register byte 2</td></tr>
<tr><td>10</td><td><a href="https://alienbill.com/2600/101/docs/stella.html#RESP">RESP0</a> </td><td colspan="8" align="center">strobe</td><td> reset player 0</td></tr>
<tr><td>11</td><td><a href="https://alienbill.com/2600/101/docs/stella.html#RESP">RESP1</a> </td><td colspan="8" align="center">strobe</td><td> reset player 1</td></tr>
<tr><td>12</td><td><a href="https://alienbill.com/2600/101/docs/stella.html#RESM">RESM0</a> </td><td colspan="8" align="center">strobe</td><td> reset missile 0</td></tr>
<tr><td>13</td><td><a href="https://alienbill.com/2600/101/docs/stella.html#RESM">RESM1</a> </td><td colspan="8" align="center">strobe</td><td> reset missile 1</td></tr>
<tr><td>14</td><td><a href="https://alienbill.com/2600/101/docs/stella.html#RESBL">RESBL</a> </td><td colspan="8" align="center">strobe</td><td> reset ball</td></tr>
<tr><td>15</td><td><a href="https://alienbill.com/2600/101/docs/stella.html#AUDC">AUDC0</a> </td><td>.</td><td>.</td><td>.</td><td>.</td><td>1</td><td>1</td><td>1</td><td>1</td><td> audio control 0</td></tr>
<tr><td>16</td><td><a href="https://alienbill.com/2600/101/docs/stella.html#AUDC">AUDC1</a> </td><td>.</td><td>.</td><td>.</td><td>1</td><td>1</td><td>1</td><td>1</td><td>1</td><td> audio control 1</td></tr>
<tr><td>17</td><td><a href="https://alienbill.com/2600/101/docs/stella.html#AUDF">AUDF0</a> </td><td>.</td><td>.</td><td>.</td><td>1</td><td>1</td><td>1</td><td>1</td><td>1</td><td> audio frequency 0</td></tr>
<tr><td>18</td><td><a href="https://alienbill.com/2600/101/docs/stella.html#AUDF">AUDF1</a> </td><td>.</td><td>.</td><td>.</td><td>.</td><td>1</td><td>1</td><td>1</td><td>1</td><td> audio frequency 1</td></tr>
<tr><td>19</td><td><a href="https://alienbill.com/2600/101/docs/stella.html#AUDV">AUDV0</a> </td><td>.</td><td>.</td><td>.</td><td>.</td><td>1</td><td>1</td><td>1</td><td>1</td><td> audio volume 0</td></tr>
<tr><td>1A</td><td><a href="https://alienbill.com/2600/101/docs/stella.html#AUDV">AUDV1</a> </td><td>.</td><td>.</td><td>.</td><td>.</td><td>1</td><td>1</td><td>1</td><td>1</td><td> audio volume 1</td></tr>
<tr><td>1B</td><td><a href="https://alienbill.com/2600/101/docs/stella.html#GRP">GRP0</a> </td><td>1</td><td>1</td><td>1</td><td>1</td><td>1</td><td>1</td><td>1</td><td>1</td><td> graphics player 0</td></tr>
<tr><td>1C</td><td><a href="https://alienbill.com/2600/101/docs/stella.html#GRP">GRP1</a> </td><td>1</td><td>1</td><td>1</td><td>1</td><td>1</td><td>1</td><td>1</td><td>1</td><td> graphics player 1</td></tr>
<tr><td>1D</td><td><a href="https://alienbill.com/2600/101/docs/stella.html#ENAM">ENAM0</a> </td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td>1</td><td>.</td><td> graphics (enable) missile 0</td></tr>
<tr><td>1E</td><td><a href="https://alienbill.com/2600/101/docs/stella.html#ENAM">ENAM1</a> </td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td>1</td><td>.</td><td> graphics (enable) missile 1</td></tr>
<tr><td>1F</td><td><a href="https://alienbill.com/2600/101/docs/stella.html#ENABL">ENABL</a> </td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td>1</td><td>.</td><td> graphics (enable) ball</td></tr>
<tr><td>20</td><td><a href="https://alienbill.com/2600/101/docs/stella.html#HMP">HMP0</a> </td><td>1</td><td>1</td><td>1</td><td>1</td><td>.</td><td>.</td><td>.</td><td>.</td><td> horizontal motion player 0</td></tr>
<tr><td>21</td><td><a href="https://alienbill.com/2600/101/docs/stella.html#HMP">HMP1</a> </td><td>1</td><td>1</td><td>1</td><td>1</td><td>.</td><td>.</td><td>.</td><td>.</td><td> horizontal motion player 1</td></tr>
<tr><td>22</td><td><a href="https://alienbill.com/2600/101/docs/stella.html#HMM">HMM0</a> </td><td>1</td><td>1</td><td>1</td><td>1</td><td>.</td><td>.</td><td>.</td><td>.</td><td> horizontal motion missile 0</td></tr>
<tr><td>23</td><td><a href="https://alienbill.com/2600/101/docs/stella.html#HMM">HMM1</a> </td><td>1</td><td>1</td><td>1</td><td>1</td><td>.</td><td>.</td><td>.</td><td>.</td><td> horizontal motion missile 1</td></tr>
<tr><td>24</td><td><a href="https://alienbill.com/2600/101/docs/stella.html#HMBL">HMBL</a> </td><td>1</td><td>1</td><td>1</td><td>1</td><td>.</td><td>.</td><td>.</td><td>.</td><td> horizontal motion ball</td></tr>
<tr><td>25</td><td><a href="https://alienbill.com/2600/101/docs/stella.html#VDELP">VDELP0</a> </td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td>1</td><td> vertical delay player 0</td></tr>
<tr><td>26</td><td><a href="https://alienbill.com/2600/101/docs/stella.html#VDELP">VDELP1</a> </td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td>1</td><td> vertical delay player 1</td></tr>
<tr><td>27</td><td><a href="https://alienbill.com/2600/101/docs/stella.html#VDELBL">VDELBL</a> </td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td>1</td><td> vertical delay ball</td></tr>
<tr><td>28</td><td><a href="https://alienbill.com/2600/101/docs/stella.html#RESMP">RESMP0</a> </td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td>1</td><td>.</td><td> reset missile 0 to player 0</td></tr>
<tr><td>29</td><td><a href="https://alienbill.com/2600/101/docs/stella.html#RESMP">RESMP1</a> </td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td>1</td><td>.</td><td> reset missile 1 to player 1</td></tr>
<tr><td>2A</td><td><a href="https://alienbill.com/2600/101/docs/stella.html#HMOVE">HMOVE</a> </td><td colspan="8" align="center">strobe</td><td> apply horizontal motion</td></tr>
<tr><td>2B</td><td><a href="https://alienbill.com/2600/101/docs/stella.html#HMCLR">HMCLR</a> </td><td colspan="8" align="center">strobe</td><td> clear horizontal motion registers</td></tr>
<tr><td>2C</td><td><a href="https://alienbill.com/2600/101/docs/stella.html#CXCLR">CXCLR</a> </td><td colspan="8" align="center">strobe</td><td> clear collision latches</td></tr>
</tbody></table>
</blockquote>
<p>
</p><hr>
<p>
<a name="rsummary"></a>
</p><h3>TIA READ ADDRESS SUMMARY</h3>
<blockquote>
<table border="1">
<tbody><tr><td>6-bit Address</td><td>Address Name </td><td>7</td><td>6</td><td>5</td><td>4</td><td>3</td><td>2</td><td>1</td><td>0</td><td> Function</td><td>D7</td><td>D6</td></tr>
<tr><td>0</td><td>CXM0P </td><td>1</td><td>1</td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td> read collision </td><td>M0 P1 </td><td>M0 P0</td></tr>
<tr><td>1</td><td>CXM1P </td><td>1</td><td>1</td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td> read collision </td><td>M1 P0 </td><td>M1 P1</td></tr>
<tr><td>2</td><td>CXP0FB </td><td>1</td><td>1</td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td> read collision </td><td>P0 PF </td><td>P0 BL</td></tr>
<tr><td>3</td><td>CXP1FB </td><td>1</td><td>1</td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td> read collision </td><td>P1 PF </td><td>P1 BL</td></tr>
<tr><td>4</td><td>CXM0FB </td><td>1</td><td>1</td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td> read collision </td><td>M0 PF </td><td>M0 BL</td></tr>
<tr><td>5</td><td>CXM1FB </td><td>1</td><td>1</td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td> read collision </td><td>M1 PF </td><td>M1 BL</td></tr>
<tr><td>6</td><td>CXBLPF </td><td>1</td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td> read collision </td><td>BL PF </td><td>unused</td></tr>
<tr><td>7</td><td>CXPPMM </td><td>1</td><td>1</td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td> read collision </td><td>P0 P1 </td><td>M0 M1</td></tr>
<tr><td>8</td><td>INPT0 </td><td>1</td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td colspan="3"> read pot port</td></tr>
<tr><td>9</td><td>INPT1 </td><td>1</td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td colspan="3"> read pot port</td></tr>
<tr><td>A</td><td>INPT2 </td><td>1</td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td colspan="3"> read pot port</td></tr>
<tr><td>B</td><td>INPT3 </td><td>1</td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td colspan="3"> read pot port</td></tr>
<tr><td>C</td><td>INPT4 </td><td>1</td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td colspan="3"> read input</td></tr>
<tr><td>D</td><td>INPT5 </td><td>1</td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td>.</td><td colspan="3"> read input</td></tr>
</tbody></table>
Note : I0, I2, I2, I3 can be grounded
under software control.
I4, I5 can be converted to latched
inputs under software control
</blockquote>
<p>
<i>(For PIA I/O addresses, see section <a href="https://alienbill.com/2600/101/docs/stella.html#pia6.0">6,0</a> --BW)</i>
</p><p>
</p><hr>
<p>
<a name="ednotes"></a>
Editor's Notes</p><p>
<i>(This section is *not* part of the manual, so you can ignore it if
you want! --BW)</i>
</p><blockquote>
I did this HTML version of the Stella Programming Guide for a couple of
reasons:
<ul>
<li>
The existing PDF version is great, but I really hate having to use a PDF
reader to read it. HTML is (supposedly) cross-platform, and since I already
keep 10-15 browser windows open at any given time, I'd rather use the same
GUI for reading the Stella docs as I do for everything else that's graphical.
</li><li>
The existing plain-text version I found is ok, but it's missing all the
diagrams (of course), and some of the text formatting is a bit strange.
</li><li>
I tried numerous programs that claim to convert PDF (or PostScript) to HTML,
but they all produced ugly, unusable results.
</li><li>
I wanted internal links in the document, such as the table of contents. The
existing PDF version doesn't seem to have them. The next version of this
document will probably have links to external `how-to' docs, with code
snippets and such.
</li><li>
The Stella/Atari development community are some of the nicest people I've
ever met, and this is my attempt to give back to the community in some small
way.
</li><li>
Finally, I needed an excuse to procrastinate... my poor 2600 game is in a
nasty state of disrepair, and I'm at the point where I'd be better starting
from scratch. Taking a break from 6502 asm and writing in a `language' like
HTML gives me a much-needed breather.
</li></ul>
<p>
The original PDF version has a few typos. I don't know if those are in the
original paper version, or mistakes in the transcription, but I fixed as many
of them as I could find (most of them were silly, like <i>it's</i> instead of
<i>its</i>, or <i>sidable</i> for <i>disable</i>). Also, I didn't try to
format the tables exactly as they appear in the PDF version, since HTML isn't
much good for that sort of thing anyway. I did my best to preserve the content,
but took a few liberties with the presentation.</p><p>
Although I have tried to avoid it, I'm sure I introduced a few errors and
typos of my own. If anybody spots one, let me know, and I'll fix it ASAP.</p><p>
As far as copyright goes, who knows what the official, legal status of the
Stella Programmer's Guide is? I sure don't. But this HTML version is free for
anyone to use and/or redistribute, as much as the original version is. If
you modify this version, I'd really appreciate it if you'd clearly mark your
new version as modified. Better yet, if you fix some of my mistakes, show me
what I did wrong so I can learn from them!</p><p>
I looked at this in Netscape 4.7, Opera 5.0b6, and Konqueror 2.1 on Linux, and IE 5.0 on Win98; it looks OK on all of them.
If you have any problems with the HTML formatting, please let me know. I tried to
use `bog standard' HTML as much as possible, so it should work OK on any
browser, on any OS, but if it doesn't, I'll fix it the best I am able.</p><p>
B. Watson<br>
atari@hardcoders.org<br>
09/15/2001<br>
</p></blockquote></blockquote></body></html>
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