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Peripherals and models description improved and expanded

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Ilia Sharin 2026-04-25 14:51:45 -04:00
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01_hardware/common/cia_chips.md
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@ -144,9 +144,75 @@ Direct CIA programming should be done with `ciaa`/`ciab` resource claims via `Op
/* ciaa.ciapra, ciaa.ciaprb, ciaa.ciaicr, ciaa.ciacra, ... */
```
## Per-Model CIA Wiring Variations
While CIA-A and CIA-B register layouts are identical across all Amigas, the **physical wiring** of their port pins varies by model:
### CIA-A Port A Differences
| Bit | Standard (A500/A2000/A1200/A4000) | A1000 | CDTV | CD32 |
|---|---|---|---|---|
| 7 | `/FIR1` — joystick 1 fire | Same | Same | **CD32 pad button** (via shift register) |
| 6 | `/FIR0` — joystick 0 fire | Same | Same | **CD32 pad button** (via shift register) |
| 5 | `/RDY` — floppy ready | Same | No internal floppy | No floppy |
| 4 | `/TK0` — track 0 sensor | Same | No internal floppy | No floppy |
| 3 | `/WPRO` — write protect | Same | No internal floppy | No floppy |
| 2 | `/CHNG` — disk change | Same | No internal floppy | No floppy |
| 1 | `/LED` — power LED | Same | Front panel LED | Front panel LED |
| 0 | `/OVL` — Chip RAM overlay | Same | Same | Same |
### CIA-A `/FLG` Pin
| Model | `/FLG` Source |
|---|---|
| A500/A2000/A3000 | Directly accessible for parallel port `BUSY` or expansion |
| A600/A1200 | **Gayle interrupt routing** — IDE and PCMCIA interrupts arrive here |
| CDTV | **IR remote receiver** — IR data packets trigger `/FLG` |
| CD32 | **Akiko interrupt routing** — CD-ROM and NVRAM events |
### CIA-B Port A (Floppy Drive Selection)
| Bit | Standard | CDTV | CD32 |
|---|---|---|---|
| 7 | `/MTR` — motor | N/A (no internal floppy) | N/A |
| 6–3 | `/SEL3`–`/SEL0` — drive select | External floppy only (`/SEL0`) | N/A |
| 2 | `/SIDE` — head side | N/A | N/A |
| 1 | `/DIR` — step direction | N/A | N/A |
| 0 | `/STEP` — step pulse | N/A | N/A |
> [!NOTE]
> On CDTV and CD32, the CIA-B floppy control bits are electrically disconnected from any drive hardware. Writing to them has no effect. If an external floppy is connected (CDTV with external drive, or CD32 with SX-1), only `/SEL0` and related signals are active.
### CD32 Gamepad — CIA Shift Register Protocol
The CD32 gamepad uses CIA-A's **Serial Data Register (SDR)** for button reads. The controller contains a shift register that is clocked via the joystick port pin 5:
```asm
; Read CD32 gamepad buttons
; Returns 7 button bits in d0
move.b #$FF, $BFE301 ; CIA-A DDRA: all outputs (temporarily)
bset #6, $BFE001 ; Pin 5 high (clock start)
bclr #6, $BFE001 ; Pin 5 low → latch button state
; Clock in 7 bits via pin toggling
moveq #6, d1
.read_pad:
bset #6, $BFE001 ; clock pulse high
btst #0, $BFE001 ; read data bit
bclr #6, $BFE001 ; clock pulse low
roxl.b #1, d0 ; shift into result
dbf d1, .read_pad
```
Standard 2-button Atari joysticks ignore the clock signal and remain fully compatible.
---
## References
- MOS Technology 6526/8520 datasheet
- ADCD 2.1 Hardware Manual — CIA chapter: http://amigadev.elowar.com/read/ADCD_2.1/Hardware_Manual_guide/
- NDK39: `hardware/cia.h`, `resources/cia.h`
- Autodocs: `cia` resource — http://amigadev.elowar.com/read/ADCD_2.1/Includes_and_Autodocs_3._guide/node00C7.html