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EightBit/M6532/inc/M6532.h
Adrian Conlon 9755a5fcd2 Add the concept of a clocked chip
2019-01-10 22:23:51 +00:00

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#pragma once
#include <cstdint>
#include <ClockedChip.h>
/*
PIA 6532 combined timer, IO and 128 bytes RAM
=============================================
MOS 6532 pin configuration
--------------------------
____________
| |_| |
VSS -| 1 40|- A6
| |
A5 -| 2 39|- theta 2
| |
A4 -| 3 38|- CS1
| | ___
A3 -| 4 37|- CS2
| | __
A2 -| 5 36|- RS
| |
A1 -| 6 35|- R/W
| | ___
A0 -| 7 34|- RES
| |
PA0 -| 8 33|- D0
| |
PA1 -| 9 32|- D1
| |
PA2 -|10 31|- D2
| |
PA3 -|11 30|- D3
| |
PA4 -|12 29|- D4
| |
PA5 -|13 28|- D5
| |
PA6 -|14 27|- D6
| |
PA7 -|15 26|- D7
| | ___
PB7 -|16 25|- IRQ
| |
PB6 -|17 24|- PB0
| |
PB5 -|18 23|- PB1
| |
PB4 -|19 22|- PB2
| |
Vcc -|20 21|- PB3
|____________|
VSS = power
A0-A6 = address
PA0-PA7 = port A
PB0-PB7 = port B
Vcc = ground
theta 2 = clock input
CS1 = chip select 1
CS2 = chip select 2 (low)
RS = RAM select (low)
R/W = read/write
RES = reset (low)
D0 - D7 = data
IRQ = interrupt request (low)
MOS 6532 Block Diagram
======================
___________ _____________
D0 <---->| | __ | DATA |
D1 <---->| DATA | ||<---->| DIRECTION |
D2 <---->| BUS | || | CONTROL |
D3 <---->| BUFFER |<---->|| | REGISTER |
D4 <---->| | || | A |
D5 <---->| | || |_____________|-----
D6 <---->| | || |
D7 <---->|___________| || _____________ |
|| | OUTPUT | |
___________ ||<---->| REGISTER A | |
CS1 ---->| | || |_____________| |
___ | CHIP | || | |
CS2 ---->| SELECT | || V |
| R/W | || _____________ |
02 ---->| | || | |<----
| | || | PERIPHERAL |<----> PA7
R/W ---->| | || | DATA |<----> PA6
___ | | ||<-----| BUFFER |<----> PA5
RES ---->|___________| || | A |<----> PA4
|| | |<----> PA3
___________ || | |<----> PA2
__ | 128 x 8 | || | |<----> PA1
RS ---->| RAM |<---->|| |_____________|<----> PA0
|___________| ||
|| _____________
|| | |<----> PB7
___________ || | PERIPHERAL |<----> PB6
___ | INTERRUPT | || | DATA |<----> PB5
IRQ ---->| CONTROL |<---->||<-----| BUFFER |<----> PB4
|___________| || | B |<----> PB3
^ || | |<----> PB2
| || | |<----> PB1
V || | |<----> PB0
___________ || |_____________|<----
| INTERVAL | || | |
| TIMER |<---->|| V |
|___________| || _____________ |
___________ || | OUTPUT | |
A0 ---->| | ||<---->| REGISTER B | |
A1 ---->| | || |_____________| |
A2 ---->| ADDRESS | || |
A3 ---->| DECODERS | || _____________ |
A4 ---->| | || | DATA |-----
A5 ---->| | || | DIRECTION |
A6 ---->|___________| ||<---->| CONTROL |
-- | REGISTER |
| B |
|_____________|
Basic Elements of Interval Timer
--------------------------------
R/W PA7 A3 D7 D6 D5 D4 D3 D2 D1 D0 R/W A1 A0
| | | | | | | | | | | | | |
V V V V V V V V V V V | V V
+---------------+ +-----------------------------------+ | +---------------+
___ | | | |<---+----->| |<---- theta 2
IRQ <---| Interrupt |<------| Programmable | | Divide |
| Control | | Register | | Down |
| | | |<----------| |
+---------------+ +-----------------------------------+ +---------------+
| | | | | | | | | |
+-----------------------+ | | | | | | |
| | | | | | | | |
| +-------------------+ | | | | | |
| | | | | | | |
V V V V V V V V
D7 D6 D5 D4 D3 D2 D1 D0
RAM<41>128 Bytes (1024 Bits)
The 128 x 8 Read/Write memory acts as a conventional static RAM. Data can be written into the RAM from
the microprocessor by selecting the chip (CS1 = 1, CS2 = 0) and by setting RS to a logic 0 (0.4v). Address
lines AO through A6 are then used to select the desired byte of storage.
Addressing Decode
-----------------
__
RS R/W A4 A3 A2 A1 A0
Write RAM 0 0 - - - - -
Read RAM 0 1 - - - - -
Write DDRA 1 0 - - 0 0 1
Read DDRA 1 1 - - 0 0 1
Write DDRB 1 0 - - 0 1 1
Read DDRB 1 1 - - 0 1 1
Write Output Reg A 1 0 - - 0 0 0
Read Output Reg A 1 1 - - 0 0 0
Write Output Reg B 1 0 - - 0 1 0
Read Output Reg B 1 1 - - 0 1 0
Write Timer
+ 1T 1 0 1 (a) 1 0 0
+ 8T 1 0 1 (a) 1 0 1
+ 64T 1 0 1 (a) 1 1 0
+ 1024T 1 0 1 (a) 1 1 1
Read Timer 1 1 - (a) 1 <09> 0
Read Interrupt Flag(s) 1 1 <09> <09> 1 <09> 1
Write Edge Detect Control 1 0 0 <09> 1 (b) (c)
(a) A3 = 0 to disable interrupt trom timer to IRQ
A3 = 1 to enable interrupt from timer to IRQ
(b) A1 = 0 to disable interrupt from PA7 to IRQ
A1 = 1 to enable interrupt from PA7 to IRQ
(c) A0 = 0 for negative edge-detect
AO = 1 for positive edge-detect
*/
namespace EightBit {
class M6532 final : public ClockedChip {
public:
M6532() noexcept;
virtual ~M6532() = default;
/* ___
Reset (RES)
During system initialization a logic "0" on the RES input will cause a zeroing of all four I/O registers. This
in turn will cause all I/O buses to act as inputs thus protecting external components from possible damage
and erroneous data while the system is being configured under software control. The Data Bus Buffers are
put into an OFF-STATE during Reset. Interrupt capability is disabled with the RES signal. The RES signal
must be held low for at least one clock period when reset is required.
*/
PinLevel& RES() { return m_res; }
/*
Read/Write (R/W)
The R/W signal is supplied by the microprocessor array and is used to control the transfer of data to and
from the microprocessor array and the 6532. A high on the R/W pin allows the processor to read (with proper
addressing) the data supplied by the 6532. A low on the R/W pin allows a write (with proper addressing) to
the 6532.
*/
PinLevel& RW() { return m_rw; }
/* ___
Interrupt Request (IRQ)
The IRQ pin is an interrupt pin from the interrupt control logic. The pin will be normally high with a low indicating
an interrupt from the 6532. An external pull-up device is required. The IRQ pin may be activated by a
transition on PA7 or timeout of the interval timer.
*/
PinLevel& IRQ() { return m_irq; }
/*
Data Bus (D0-D7)
The 6532 has eight bi-directional data pins (D0-D7). These pins connect to the system's data lines and
allow transfer of data to and from the microprocessor array. The output buffers remain in the off state except
when a Read operation occurs and are capable of driving one standard TTL load and 130 pf.
*/
uint8_t& data() { return m_data; }
/*
Peripheral Data Ports
The 6532 has 16 pins available for peripheral I/O operations. Each pin is individually software programmable
to act as either an input or an output. The 16 pins are divided into 2 8-bit ports, PA0-PA7 and PB0-PB7.
PA7 also has other uses which are discussed in later sections. The pins are set up as an input by writing a
"0" into the corresponding bit of the data direction register. A "1" into the data direction register will cause
its corresponding bit to be an output. When in the input mode, the peripheral output buffers are in the "1"
state and pull-up device acts as less than one TTL load to the peripheral data lines. On a Read operation, the
microprocessor unit reads the peripheral pin. When the peripheral device gets information from the 6532 it
receives data stored in the data register. The microprocessor will read correct information if the peripheral
lines are greater than 2.0 volts for a "1" and less than 0.8 volts for a "0" as the peripheral pins are all TTL
compatible. Pins PB0-PB7 are also capable of sourcing 3 ma at 1.5v, thus making them capable of Darlington
drive.
*/
uint8_t& PA() { return m_pa; }
uint8_t& PB() { return m_pb; }
/*
Address Lines (A0-A6)
There are 7 address pins. In addition to these 7, there is 9 RAM SELECT pin. These pins, A0-A6 and RAM
SELECT, are always used as addressing pins. There are two additional pins which are used as CHIP
SELECTS. They are pins CS1 and CS2.
*/
uint8_t& address() { return m_address; }
// RAM SELECT, active low
PinLevel& RS() { return m_rs; }
// CHIP SELECT 1, active high
PinLevel& CS1() { return m_cs1; }
// CHIP SELECT 2, active low
PinLevel& CS2() { return m_cs2; }
void tick();
virtual void initialise() final;
void reset();
private:
enum EdgeDetect { Positive, Negative };
enum TimerIncrement { One = 1, Eight = 8, SixtyFour = 64, OneThousandAndTwentyFour = 1024 };
auto& RAM() { return m_ram; }
auto& DDRA() { return m_ddra; }
auto& DDRB() { return m_ddrb; }
auto& IF() { return m_interruptFlags; }
bool selected() { return raised(CS1()) && lowered(CS2()); }
uint8_t m_address;
uint8_t m_data;
uint8_t m_pa;
uint8_t m_dra;
uint8_t m_ddra;
uint8_t m_pb;
uint8_t m_drb;
uint8_t m_ddrb;
PinLevel m_res;
PinLevel m_rw;
PinLevel m_irq;
PinLevel m_rs;
PinLevel m_cs1;
PinLevel m_cs2;
Ram m_ram = 0x80;
bool m_allowTimerInterrupts;
bool m_allowPA7Interrupts;
EdgeDetect m_edgeDetection;
TimerIncrement m_timerIncrement;
uint8_t m_currentIncrement;
uint8_t m_timerInterval;
bool m_timerInterrupt;
uint8_t m_interruptFlags;
};
}
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