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TABLE OF CONTENTS 4
STELLA
PROGRAMMER'S
GUIDE
by
Steve Wright
12/03/79
(Reconstructed by Charles Sinnett 6/11/93 Internet:
cas@mentor.cc.purdue.edu)
Table of Contents
TELEVISION PROTOCOL 1
Diagram 1 - Atari TV Frame 2
The TIA (as seen by the programmer) 3
1.0 General Description 3
2.0 The Registers 3
3.0 Synchronization 4
3.1 Horizontal Timing 4
3.2 Microprocessor Synchronization 4
3.3 Vertical timing 4
4.0 Color and Luminosity 5
5.0 Playfield 5
6.0 The Moveable Objects Graphics 6
6.1 Missile Graphics (M0, M1) 6
6.2 Ball Graphics (BL) 6
6.3 Player Graphics (P0, P1) 7
7.0 Horizontal Positioning 8
8.0 Horizontal Motion 8
9.0 Object Priorities 9
10.0 Collisions 10
11.0 Sound 10
11.1 Tone 10
11.2 Frequency 10
11.3 Volume 10
12.0 Input Ports 11
12.1 Dumped Input Ports (INPT0 thru INPT3) 11
12.2 Latched Input Ports (INPT4, INPT5) 11
THE PIA (6532) 12
1.0 General 12
2.0 Interval timer 12
2.1 Setting the timer 12
2.2 Reading the timer 12
2.3 When the timer reaches zero 12
3.0 RAM 13
4.0 The I/O ports 13
4.1 Port B - Console Switches (read only) 13
5.0 Port A - Hand Controllers 13
5.1 Setting for input or output 13
5.2 Inputting and Outputting 14
5.3 Joystick Controllers 14
5.4 Paddle (pot) controllers 14
5.5 Keyboard controllers 15
6.0 Address summary table 15
PAL/SECAM CONVERSIONS 16
PAL 16
SECAM 16
TIA 1A - TELEVISION INTERFACE ADAPTOR (MODEL 1A) 17
GENERAL DESCRIPTION 17
DETAILED DESCRIPTION 18
1. Data and addressing 18
2. Synchronization 18
A. Horizontal Timing 18
B. Vertical Timing 18
C. Composite Sync 18
D. Microprocessor Synchronization 19
3. Playfield graphics Register 19
A. Description 19
B. Normal Serial Output 19
C. Reflected Serial Output 19
D. Timing Constraints 20
4. Horizontal Position Counters 20
A. Description 20
B. Ball position Counter 20
C. Player Position Counters 20
D. Missile Position Counters 21
5. Horizontal Motion Registers 21
A. General Description 21
B. Timing constraints 21
6. Moving Object Graphics Registers 22
A. General Description 22
B. Missile Graphics 22
C. Player Graphics 22
D. Vertical Delay 23
E. Ball Graphics 24
7. Collision Detection Latches 24
A. Definitions 24
B. Reading Collision 24
C. Reset 24
8. Input ports 25
A. General Description 25
B. Dumped Input Ports (I0 through I3) 25
C. Latched Input ports (I4, I5) 25
8.5 Priority Encoder 26
A. Purpose 26
B. Priority Assignment 26
C. Priority Control 26
9 Color Luminance Registers 27
A. Description 27
B. Multiplexing 27
10. Color Phase Shifter 27
11. Audio Circuits 27
A. Frequency Select 27
B. Noise-Tone Generator 28
C. Volume Select 28
Figure 1. Vertical Delay 29
Figure 2. Synchronization 30
Figure 3. Color-Luminance 30
Figure 4. Typical Horizontal Motion Circuit 31
Figure 5. Playfield Graphics 32
Figure 6. Collision Detection 33
Figure 7. Audio Circuit 34
Figure 8. Input Ports 35
Figure 9. Game System 36
Write Address Detailed Functions 37
WSYNC (wait for sync) 37
RSYNC (reset sync) 37
VSYNC 37
VBLANK 37
PJ0 (PF1, PF2) 38
PLAYFIELD REGISTERS SERIAL OUTPUT 38
CTRLPF 38
NUSIZ0 (NUSIZ1) 39
RESP0 (RESP1, RESM0, RESM1, RESBL) 39
RESMP0 (RESMP1) 39
HMOVE 40
HMCLR 40
HMP0 (HMP1, HMM0, HMM1, HMBL) 40
ENAM0 (ENAM1, ENABL) 41
GRP0 (GRP1) 41
REFP0 (REFP1) 41
VDELP0 (VDELP1, VDELBL) 41
CXCLR 41
COLUP0 (COLUP1, COLUPF, COLUBK) 42
AUDF0 (AUDF1) 42
AUDC0 (AUDC1) 43
AUDV0 (AUDV1) 43
WRITE ADDRESS SUMMARY 44
READ ADDRESS SUMMARY 45
TIA O0..02 AND LUM TIMING 46
TIA WRITE TIMING CHARACTERISTICS 47
TIA READ TIMING CHARACTERISTICS 48
TIA COMP-SYN AND READY TIMING 49
RSYNC, RES0O, H01, H02, SHB, 02, 0O 50
TIA RSYNC AND BLANK AND READY TIMING 51
TELEVISION PROTOCOL
(The TV picture according to Atari)
For the purposes of Stella programming, a single television
<20>frame<6D> 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 <20>frame<6D> (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<72>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.
All horizontal timing is taken care of by hardware, but the
microprocessor must <20>manually<6C> 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.
* (to signal the TV set to start a new frame)
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 <20>one step ahead<61> 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 <20>Kernel<65>, as it is the essence or kernel of the game.
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.
Diagram 1 - Atari TV Frame
The TIA (as seen by the programmer)
1.0 General Description
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 <20>playfield<6C>
and 5 moveable objects can be created and manipulated by
software.
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 <20>move<76>.
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.
2.0 The Registers
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.
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
<20>strobe<62> or trigger events. A <20>strobe<62> 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.
3.0 Synchronization
3.1 Horizontal Timing
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 <20>color clocks<6B> 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.
3.2 Microprocessor Synchronization
The microprocessor<6F>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 WSYNC (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.
NOTE: WSYNC and all the following addresses<65> bit
structures are itemized in the TIA hardware manual. The
purpose of this document is to make them understandable.
3.3 Vertical timing
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 <20>1<EFBFBD> in D1 of VSYNC to turn it on, count at least 2 scan
lines, then write a <20>0<EFBFBD> to D1 of VSYNC to turn it off.
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 <20>1<EFBFBD>
in D1 of VBLANK to turn it on, count 37 lines, then write a
<20>0<EFBFBD> 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.
4.0 Color and Luminosity
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:
color-lum register Objects colored
COLUMP0 P0, M0 (player 0, missile 0)
COLUMP1 P1, M1 (player 1, missile 1)
COLUMPF PF, BL (playfield, ball)
COLUMBK BK (background)
For example, if the COLUMP0 register is set for light red,
both P0 and M0 will be light red when drawn.
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 <20>strobe<62> registers), the data written to them
is latched until altered by another write operation.
5.0 Playfield
The PF 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.
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 <20>bits<74> of the playfield,
starting at the left edge of the TV screen. PF1 constructs
the next 8 <20>bits<74>, and PF2 the last 8 bits<74> which end at
the center of the screen. The PF register is scanned from
left to right and where a <20>1<EFBFBD> is found the PF color is
drawn, and where a <20>0<EFBFBD> is found, the BK color is drawn. To
clear the playfield, obviously zeros must be written into
PF0, PF1, and PF2.
To make the right half of the playfield into a duplication
or copy of the left half, a <20>0<EFBFBD> is written to D0 of the
CTLPF (control playfield) register. Writing a <20>1<EFBFBD> will
cause the reflection to be displayed.
6.0 The Moveable Objects Graphics
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 <20>thick<63>. 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<74> own characteristics and
limitations.
6.1 Missile Graphics (M0, M1)
The two missile graphics registers will draw a missile on
any scan line by writing a <20>1<EFBFBD> to the one bit enable
missile registers (ENAM0, ENAM1). Writing a <20>0<EFBFBD> to these
registers will disable the graphics. The missiles<65> 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 (NUSIZ0,
NUSIZ1). This has the effect of <20>stretching<6E> the missile
out over 1,2,4, or 8 color clock counts (a full scan line
is 160 color clocks).
6.2 Ball Graphics (BL)
The ball graphics register works just like the missile
registers. Writing a <20>1<EFBFBD> to the enable ball register
(ENABL) enables the ball graphics until the register is
disabled. The ball can also be <20>stretched<65> to widths of 1,
2, 4, or 8 color clock counts by writing to bits D4 and D5
of the CTRLPF register.
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 <20>1<EFBFBD> to D0 of the vertical delay
(VDELBL) 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 <20>jumps<70>. The use of vertical delay
allows the objects to move one scan line at a time.
6.3 Player Graphics (P0, P1)
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 <20>shape<70> 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.
The player graphics are drawn line-by-line like all other
graphics. The difference here is each scan line of the
player is 8 <20>bits<74> wide, whereas the missiles and ball are
one <20>bit<69> wide. Therefore, a player can be though of as
being drawn of graph paper 8 squares wide and as tall as
desired. To <20>color in the squares<65> of this imaginary graph
paper, 8 data bits are written into the players graphics
registers (GP0, GP1). This 8 bit register is scanned from
D7 to D0, and wherever a <20>1<EFBFBD> is found that <20>square<72> gets
the players<72> color (from the color-lum register) and where
a <20>0<EFBFBD> is found that <20>square<72> gets the background color. To
position a player vertically, simply leave all <20>0<EFBFBD>s<EFBFBD> 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 <20>0<EFBFBD>s<EFBFBD> to turn
off the players<72> graphics until the end of that frame.
To display a mirror image (reflection) instead of the
original figure, write a <20>1<EFBFBD> to D3 of the one bit
reflection register (REFP0, REFP1). A <20>0<EFBFBD> written to these
registers restores the original figure.
Multiple copies of players as well as their size are
controlled by writing 3 bits (D0, D1, D2) into the number-
size registers (NUSIZ0, 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 <20>square<72> 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.
Vertical delay for the players works exactly like the ball
by writing a <20>1<EFBFBD> to D0 in the players<72> vertical delay
registers (VDELP0, VDELP1). Writing a <20>0<EFBFBD> to these
locations disables the vertical delay.
7.0 Horizontal Positioning
The horizontal position of each object is set by writing to
its<74> associated reset register (RESP0, RESP1, RESM0, RESM1,
RESBL) which are all <20>strobe<62> 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<69> on the next scan line.
Whether or not P0 is actually drawn on the screen is a
function of the data in the GP0 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 <20>course<73>
positioning is <20>fine tuned<65> by the Horizontal Motion,
explained in section 8.0.
Missiles have an additional positioning command. Writing a
<20>1<EFBFBD> to D1 of the reset missile-to-player register (RESMP0,
RESMP1) disables that missiles<65> graphics (turns it off) and
repositions it horizontally to the center of its<74>
associated player. Until a <20>0<EFBFBD> is written to the register,
the missiles<65> horizontal position is locked to the center
of its<74> player in preparation to be fired again.
8.0 Horizontal Motion
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 (HMP0, HMP1, HMM0, HMM1, HMBL) that can be loaded
with a value in the range of +7 to -8 (negative values are
expressed in two<77>s complement from). This motion is not
executed until the HMOVE 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 (HMCLR).
There are timing constraints for the HMOVE command. The
HMOVE command must immediately follow a WSYNC (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.
9.0 Object Priorities
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.
Priority Objects
1 P0, M0
2 P1, M1
3 BL, PF
4 BK
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 CTRLPF register. The following table
illustrates how the priorities are affected:
Priority Objects
1 PF, BL
2 P0, M0
3 P1, M1
4 BK
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 PF
graphics register, and the score will be in the same color
as its associated player.
10.0 Collisions
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 (CXCLR).
11.0 Sound
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.
11.1 Tone
The noise-tone generator is controlled by writing to the 4
bit audio control registers (AUDC0, 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".
11.2 Frequency
Frequency selection is controlled by writing to a 5 bit
audio frequency register (AUDF0, 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.
11.3 Volume
Volume is controlled by writing to a 4 bit audio volume
register (AUDV0, AUDV1). Writing 0 to these registers
turns sound off completely, and writing any value up to 15
increases the volume accordingly.
12.0 Input Ports
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".
12.1 Dumped Input Ports (INPT0 thru INPT3)
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 VBLANK 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.
12.2 Latched Input Ports (INPT4, INPT5)
These two ports have latches that are both enabled by
writing a "1" or disabled by writing a "0" to D6 of VBLANK.
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.
THE PIA (6532)
1.0 General
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.
2.0 Interval timer
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).
2.1 Setting the timer
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 :
Hex Address Interval Mnemonic
294 1 clock TIM1T
295 8 clocks TIM8T
296 64 clocks TIM64T
297 1024 clocks T1024T
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.
2.2 Reading the timer
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.
2.3 When the timer reaches zero
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.
3.0 RAM
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).
4.0 The I/O ports
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.
4.1 Port B - Console Switches (read only)
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:
Data Bit Switch Bit Meaning
D7 P1 difficulty 0 = amateur (B), 1 = pro (A)
D6 P0 difficulty 0 = amateur (B), 1 = pro
(A)
D5/D4 (not used)
D3 color - B/W 0 = B/W, 1 = color
D2 (not used)
D1 game select 0 = switch pressed
D0 game reset 0 = switch pressed
5.0 Port A - Hand Controllers
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.
5.1 Setting for input or output
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 & PA4
would be outputs, and PA3, PA2, PA1 & PA0 would be inputs.
5.2 Inputting and Outputting
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).
5.3 Joystick Controllers
Two joysticks can be read by configuring the entire port as
input and reading the data at SWCHA according to the
following table:
Data Bit Direction Player
D7 right P0
D6 left P0
D5 down P0
D4 up P0
D3 right P1
D2 left P1
D1 down P1
D0 up P1
(P0 = left player, P1 = right player)
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.
5.4 Paddle (pot) controllers
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 :
Data Bit Paddle #
D7 P0
D6 P1
D5/D4 (not used)
D3 P2
D2 P3
D1/D0 (not used)
5.5 Keyboard controllers
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 :
Data Bit Keyboard Row Player
D7 bottom P0
D6 third P0
D5 second P0
D4 top P0
D3 bottom P1
D2 third P1
D1 second P1
D0 top P1
(P0 = left player, P1 = right player)
NOTE : a delay of 400 microseconds is necessary between
writing to this port and reading the TIA input ports.
6.0 Address summary table
Hex Address Mnemonic Purpose
280 SWCHA Port A; input or output (read or
write)
281 SWACNT Port A DDR, 0= input, 1=output
282 SWCHB Port B; console switches (read only)
283 SWBCNT Port B DDR (hardwired as input)
284 INTIM Timer output (read only)
294 TIM1T set 1 clock interval (838
nsec/interval)
295 TIM8T set 8 clock interval (6.7
usec/interval)
296 TIM64T set 64 clock interval (53.6
usec/interval)
297 T1024T set 1024 clock interval (858.2
usec/interval)
NOTE: one clock is also one microprocessor machine cycle
PAL/SECAM CONVERSIONS
PAL
1. The number of scan lines, and therefore the frame time
increases from NTSC to PAL according to the following
table:
NTSC PAL
scan micro scan micro
lines seconds lines seconds
VBLANK 40 2548 48 3085
KERNAL 192 12228 228 14656
OVERSCAN 30 1910 36 2314
FRAME 262 16686 312 20055
2. Sounds will drop a little in pitch (frequency) because
of a slower crystal clock. Some sounds may need the
AUDF0/AUDF1 touched up.
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.
SECAM
1. SECAM is a little weird. It takes the PAL software, but
the console color/black & white switch is hardwired as
black & white. Therefore, it reads the PAL black & white
tables in software and assigns a fixed color to each lum of
black & white according to the following table:
Lum Color
0 Black
2 Blue
4 Red
6 Magenta
8 green
A cyan
C yellow
E white
There is a trap here: the manual is the same for NTSC,
PAL, & SECAM. This means that the descriptions for black &
white must jive between NTSC & PAL. If you make major
changes to PAL black & white to achieve good SECAM color,
NTSC black & white must be made similar.
2. PAL sounds work fine on SECAM with one exception: when a
sound is to be turned off, it must be one by setting
AUDV0/AUDV1 to 0, not by setting AUDC0/AUDC1 to 0.
Otherwise, you get an obnoxious background sound.
TIA 1A - TELEVISION INTERFACE ADAPTOR (MODEL 1A)
GENERAL DESCRIPTION
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.
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.
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.
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.
The microprocessor determines all vertical position and
motion by writing zeros or ones into object registers
before each appropriate horizontal line.
Walls, clouds and other seldom moved objects are produced
by a low resolution data register called the playfield
register.
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.
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.
Two (2) independent audio generating circuits are included,
each with programmable frequency, noise content, and volume
control registers.
DETAILED DESCRIPTION
1. Data and addressing
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.
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.
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.
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.
2. Synchronization
A. Horizontal Timing
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.
B. Vertical Timing
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. (VSYNC, VBLANK )
C. Composite Sync
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.
D. Microprocessor Synchronization
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 WSYNC
(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.
3. Playfield graphics Register
A. Description
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 (PF0,
PFl, PF2). Playfield may be loaded at any time. To clear
the playfield, zeros must be written into all three
addresses.
B. Normal Serial Output
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.
C. Reflected Serial Output
A reflected playfield may be requested by writing a one
into bit zero of the playfield control register (CTRLPF).
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.
D. Timing Constraints
Even though the playfield bytes (PF0, 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.
4. Horizontal Position Counters
A. Description
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.
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.
All position counters can be reset to zero count by the
microprocessor at any time, by a write instruction to the
reset addresses (RESBL, RESM0, RESMl, RESP0, 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.
B. Ball position Counter
The ball position counter has only the zero crossing decode
and therefore cannot trigger multiple copies of the ball
graphics.
C. Player Position Counters
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 (NUSIZ0,
NUSIZ1), and trigger 1,2, or 3 copies of the player (at
various spacings) across a horizontal line as shown on page
___. These same control bits are used for the decodes on
the missile position counter, insuring an equal number of
players and missiles.
D. Missile Position Counters
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 (RESMP0, 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.
5. Horizontal Motion Registers
A. General Description
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 (HMP0, HMPl, HMM0, HMMl, HMBL)
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 HMOVE address
from the microprocessor. These registers may all be cleared
to zero (no motion) simultaneously by an HMCLR 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.
B. Timing constraints
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 HMOVE 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.
6. Moving Object Graphics Registers
A. General Description
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 .
B. Missile Graphics
The graphics registers for both missiles are identical and
very simple. They each consist of a one bit register called
missile enable (ENAM0, ENAM1). This graphics bit is scanned
(outputted) only when triggered by its corresponding
position counter. There are control bits (bits 4, 5, of
NUSIZ0, 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).
C. Player Graphics
The graphics registers for both players are identical and
are rather complex. They each consist of eight bit parallel
registers (GRP0, GRP1) and a bi-directional parallel to
serial scan counter that converts the parallel data into
serial output. A one bit control register (REFP0, 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.
The clock into the scan counter can be controlled (three
bits of NUSIZ0 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.
D. Vertical Delay
Each of the player graphics registers actually consists of
two 8 bit parallel registers. The first (GRP0, 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 (VDEL0, 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 GRP0 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 (VDEL0, VDELl) then select delayed or undelayed
registers for player 0 and player 1 as serial outputs.
E. Ball Graphics
The ball graphics register is almost identical to the
missile graphics register. It also consists of a single
enable bit (ENABL) whose output is triggered by the ball
position counter. It also has two control bits (bits 4, 5
of CTRLPF) 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 (VDELBL) 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 (GRP0), because GRP1 is
used to load the second enable bit from the output of the
first on alternate lines.
7. Collision Detection Latches
A. Definitions
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.
B. Reading Collision
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.
C. Reset
All collision bits are reset simultaneously by the
microprocessor using the reset address CXCLR. This is
usually done near the end of vertical blank, after
collisions have been tested.
8. Input ports
A. General Description
There are 6 input ports on this chip whose logic state may
be read on data line 7 with read addresses INPT0 through
INPT5. These 6 ports are divided into two types, "dumped"
and "latched". See Figure 8.
B. Dumped Input Ports (I0 through I3)
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 VBLANK. 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.
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.
C. Latched Input ports (I4, I5)
These two input ports have latches which can be enabled or
disabled by writing into bit 6 of register VBLANK.
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.
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.
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 VBLANK.
8.5 Priority Encoder
A. Purpose
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.
B. Priority Assignment
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 it's corresponding player (P0,
M0) and the ball is given the same color-lum value and
priority as the playfield (PF, BL).
The following table illustrates the normal priority
assignment:
Highest Priority P0, M0
Second Highest P1, M1
Third Highest PF, BL
Lowest Priority BK
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.).
C. Priority Control
There are two playfield control bits that affect priority,
one called playfield priority (PFP) (bit 2 of CTRLPF) 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.
Highest Priority PF, BL
Second Highest P0, M0
Third Highest P1, M1
Lowest Priority BK
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.
9 Color Luminance Registers
A. Description
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
(COLUP0, 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.
B. Multiplexing
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.
10. Color Phase Shifter
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.
11. Audio Circuits
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.
A. Frequency Select
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 (AUDF). 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.
B. Noise-Tone Generator
This circuit contains a nine bit shift counter which may be
controlled by the output code from a four bit audio control
register(AUDC), 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.
C. Volume Select
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
(AUDV). 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.
Figure 1. Vertical Delay
Figure 2. Synchronization
Figure 3. Color-Luminance
Figure 4. Typical Horizontal Motion Circuit
Figure 5. Playfield Graphics
Figure 6. Collision Detection
Figure 7. Audio Circuit
Figure 8. Input Ports
Figure 9. Game System
Write Address Detailed Functions
WSYNC (wait for sync)
This address halts microporcessor by clearing RDY latch to
zero. RDY is set true again by the leading edge of
horizontal blank.
Data bits not used
RSYNC (reset sync)
This address resets the horizontal sync counter to define
the beginning of horizontal blank time, and is used in chip
testing.
Data bits not used
VSYNC
This address controls vertical sync time by writing D1 into
the VSYNC latch
D1 [1 = start vert sync, 0 = stop vertical sync]
VBLANK
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.
D1 [ 1 = start vert. blank, 0 = stop vert. blank]
D6 [ 1 = Enable I4 I5 latches, 0 = disable I4 I5 latches]
D7 [ 1 = dump I6I1I2I3 ports to ground, 0 = remove dump
path to ground]
Note : Disable latches (D6 = 0) also resets latches to
logic true
PJ0 (PF1, PF2)
These addresses are used to write into playfield registers
PLAYFIELD REGISTERS SERIAL OUTPUT
1 horizontal line ( 160 clocks)
Playfield
Reflect Control
PF0 PF1 PF2 PF0 PF1 PF2
center
PF0 PF1 PF2 PF2 PF1
PF0
each bit = 4 clocks
CTRLPF
This address is uded to write into the playfield control
register (a logic 1 causes action as described below)
D0 = REF (reflect playfield)
D1 = SCORE (left half of playfield gets color of player 0,
right half gets color of player 1)
D2 = PFP (playfield gets priority over players so they can
move behind the playfield)
D4 & D5 = BALL SIZE
D5 D4 Width
0 0 1 clock
0 1 2 clocks
1 0 4 clocks
1 1 8 clocks
NUSIZ0 (NUSIZ1)
These addresses control the number and size of players and
missiles.
Missile Size D5 D4 Width
0 0 1 clock
0 1 2 clocks
1 0 4 clocks
1 1 8 clocks
Player-Missile number & player size
1/2 television line (80 clocks)
8 clocks per square
RESP0 (RESP1, RESM0, RESM1, RESBL)
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.
No data bits are used
RESMP0 (RESMP1)
These addresses are used to reset the hoiz. location of a
missile to the center of it<69>s corresponding player. As
long as this control bit is true (1) the missile will
remain locked to the center of it<69>s player and the missile
graphics will be siddabled. When a zero is written into
this location, the missile is enabled, and can be moved
independently from the player.
D1 = RESMP (missile-player reset)
HMOVE
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.
No data bits are used
HMCLR
This address clears all horizontal motion registers to zero
(no motion)
No data bits are used
HMP0 (HMP1, HMM0, HMM1, HMBL)
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 :
D7 D6 D5 D4
0 1 1 1 +7
0 1 1 0 +6
0 1 0 1 +5 Move left
0 1 0 0 +4 indicated number
0 0 1 1 +3 of clocks
0 0 1 0 +2
0 0 0 1 +1
0 0 0 0 0 No Motion
1 1 1 1 -1
1 1 1 0 -2
1 1 0 1 -3
1 1 0 0 -4 move right
1 0 1 1 -5 indicated number
1 0 1 0 -6 of clocks
1 0 0 1 -7
1 0 0 0 -8
WARNING : These motion registers should not be modified
during the 24 computer cycles immediately following an
HMOVE command. Unpredictable motion values may result.
ENAM0 (ENAM1, ENABL)
These addresses write D1 into the 1 bit missile or ball
graphics registers.
D1 - [0 = dissables object, 1 = enables object]
GRP0 (GRP1)
These addresses write data into the player graphics
registers.
Note: serial output begins with D7, unless REFP0 (REFP1) =
1
REFP0 (REFP1)
These addesses write D3 into the 1 bit player reflect
registers
D3 - [ 0 = no reflect, D7 of GRP on left, 1 = reflect, D0
of GRP on left]
VDELP0 (VDELP1, VDELBL)
These addresses write D0 into the 1 bit vertical delay
registers, to delay players or ball by one vertical line.
D0 - [0 = no delay, 1 = delay]
CXCLR
This adderess clears all collision latches to zero (no
collision)
No data bits are used
COLUP0 (COLUP1, COLUPF, COLUBK)
These addresses write data into the player, playfield, adn
background color-luminance registers
COLOR D7 D6 D5 D4 D3 D2 D1 LUM
grey - gold 0 0 0 0 0 0 0 black
0 0 0 1 0 0 1 dark grey
orange, brt-0 0 1 0 0 1 0
org
0 0 1 1 0 1 1 grey
pink - 0 1 0 0 1 0 0
purple
0 1 0 1 1 0 1
purp-blue, 0 1 1 0 1 1 0 light gret
blue
0 1 1 1 1 1 1 white
blue - lt. 1 0 0 0
blue
1 0 0 1
torq. - 1 0 1 0
grn. blue
1 0 1 1
grn. - yel. 1 1 0 0
grn.
1 1 0 1
org. grn - 1 1 1 0
lt org.
1 1 1 1
AUDF0 (AUDF1)
These addresses write data into the audio frequency divider
registers.
D4 D3 D2 D1 D0 30KHz divided
by
0 0 0 0 0 no division
0 0 0 0 1 divide by 2
0 0 0 1 0 divide by 3
.. .. .. .. .. ...
. . . . .
1 1 1 1 0 divide by 31
1 1 1 1 1 divide by 32
AUDC0 (AUDC1)
These addresses write data into the audio control registers
which control the noise content and additional division of
the audio output.
D3 D2 D1 D0 Type of noise
or division
0 0 0 0 set to 1
0 0 0 1 4 bit poly
0 0 1 0 div 15 -> 4
bit poly
0 0 1 1 5 bit poly ->
4 bit poly
0 1 0 0 div 2 : pure
tone
0 1 0 1 div 2 : pure
tone
0 1 1 0 div 31 : pure
tone
0 1 1 1 5 bit poly ->
div 2
1 0 0 0 9 bit poly
(white noise)
1 0 0 1 5 bit poly
1 0 1 0 div 31 : pure
tone
1 0 1 1 set last 4
bits to 1
1 1 0 0 div 6 : pure
tone
1 1 0 1 div 6 : pure
tone
1 1 1 0 div 93 : pure
tone
1 1 1 1 5 bit poly div
6
AUDV0 (AUDV1)
These addresses write data into the audio volume registers
which set the pull down impedance driving the audio output
pads.
D3 D2 D1 D0 Audio Output
Pull down
current
0 0 0 0 No output
current
0 0 0 1 lowest
0 0 1 0
.. .. .. ..
. . . .
1 1 1 0
1 1 1 1 highest
WRITE ADDRESS SUMMARY
6 bit Address 7 6 5 4 3 2 1 0 Function
addres Name
s
00 VSYNC 1 vertical sync set-clear
01 VBLANK 1 1 1 vertical blank set-
clear
02 WSYNC s t r o b e wait for leading edge
of horizontal blank
03 RSYNC s t r o b e reset horizontal sync
counter
04 NUSIZ0 1 1 1 1 1 1 number-size player-
missile 0
05 NUSIZ1 1 1 1 1 1 1 number-size player-
missile 1
06 COLUP0 1 1 1 1 1 1 1 color-lum player 0
07 COLUP1 1 1 1 1 1 1 1 color-lum player 1
08 COLUPF 1 1 1 1 1 1 1 color-lum playfield
09 COLUBK 1 1 1 1 1 1 1 color-lum background
0A CTRLPF 1 1 1 1 1 control playfield ball
size & collisions
0B REFP0 1 reflect player 0
0C REFP1 1 reflect player 1
0D PF0 1 1 1 1 playfield register byte
0
0E PF1 1 1 1 1 1 1 1 1 playfield register byte
1
0F PF2 1 1 1 1 1 1 1 1 playfield register byte
2
10 RESP0 s t r o b e reset player 0
11 RESP1 s t r o b e reset player 1
12 RESM0 s t r o b e reset missile 0
13 RESM1 s t r o b e reset missile 1
14 RESBL s t r o b e reset ball
15 AUDC0 1 1 1 1 audio control 0
16 AUDC1 1 1 1 1 1 audio control 1
17 AUDF0 1 1 1 1 1 audio frequency 0
18 AUDF1 1 1 1 1 audio frequency 1
19 AUDV0 1 1 1 1 audio volume 0
1A AUDV1 1 1 1 1 audio volume 1
1B GRP0 1 1 1 1 1 1 1 1 graphics player 0
1C GRP1 1 1 1 1 1 1 1 1 graphics player 1
1D ENAM0 1 graphics (enable)
missile 0
1E ENAM1 1 graphics (enable)
missile 1
1F ENABL 1 graphics (enable) ball
20 HMP0 1 1 1 1 horizontal motion
player 0
21 HMP1 1 1 1 1 horizontal motion
player 1
22 HMM0 1 1 1 1 horizontal motion
missile 0
23 HMM1 1 1 1 1 horizontal motion
missile 1
24 HMBL 1 1 1 1 horizontal motion ball
25 VDELP0 1 vertical delay player 0
26 VDEL01 1 vertical delay player 1
27 VDELBL 1 vertical delay ball
28 RESMP0 1 reset missile 0 to
player 0
29 RESMP1 1 reset missile 1 to
player 1
2A HMOVE s t r o b e apply horizontal motion
2B HMCLR s t r o b e clear horizontal motion
registers
2C CXCLR s t r o b e clear collision latches
READ ADDRESS SUMMARY
6 bit Address 7 6 5 4 3 2 1 0 Function
addres Name
s D7 D6
0 CXM0P 1 1 read MO P1 M0 P0
collision
1 CXM1P 1 1 read M1 P0 M1 P1
collision
2 CXP0FB 1 1 read P0 PF P0 BL
collision
3 CXP1FB 1 1 read P1 PF P1 BL
collision
4 CXM0FB 1 1 read M0 PF M0 BL
collision
5 CXM1FB 1 1 read M1 PF M1 BL
collision
6 CXBLPF 1 read BL PF unuse
collision d
7 CXPPMM 1 1 read P0 P1 M0 M1
collision
8 INPT0 1 read pot port
9 INPT1 1 read pot port
A INPT2 1 read pot port
B INPT3 1 read pot port
C INPT4 1 read input
D INPT5 1 read input
Note : I0, I2, I2, I3
can be grounded under
software control.
I4, I5 can be converted
to latched inputs under
software control
TIA O0..02 AND LUM TIMING
TIA WRITE TIMING CHARACTERISTICS
TIA READ TIMING CHARACTERISTICS
TIA COMP-SYN AND READY TIMING
RSYNC, RES0O, H01, H02, SHB, 02, 0O
TIA RSYNC AND BLANK AND READY TIMING
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