Difference between revisions of "Default I/O Port Summary"
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! b15 !! b14 !! b13 !! b12 !! b11 !! b10 !! b9 !! b8 !! b7 !! b6 !! b5 !! b4 !! b3 !! b2 !! b1 !! b0 | ! b15 !! b14 !! b13 !! b12 !! b11 !! b10 !! b9 !! b8 !! b7 !! b6 !! b5 !! b4 !! b3 !! b2 !! b1 !! b0 | ||
|- | |- | ||
| − | | Gate-Array || Write | + | | Gate-Array || Write only || 0 || 1 || - || - || - || - || - || - || - || - || - || - || - || - || - || - |
|- | |- | ||
| − | | RAM Configuration || Write | + | | RAM Configuration || Write only || 0 || - || - || - || - || - || - || - || - || - || - || - || - || - || - || - |
|- | |- | ||
| CRTC || Read/Write || - || 0 || - || - || - || - || r1 || r0 || - || - || - || - || - || - || - || - | | CRTC || Read/Write || - || 0 || - || - || - || - || r1 || r0 || - || - || - || - || - || - || - || - | ||
Revision as of 09:28, 10 January 2025
This list shows only the internal standard I/O ports, as used in the BIOS ROM of the CPC 464/664/6128 BIOS, and in the AMSDOS ROM of the CPC 664/6128 and DDI-1. For a more complete list, including all Peripherals, see the Complete I/O Port Summary.
Contents
[hide]I/O Port Allocation Rules
| Hardware device | Read/Write | Port bits | |||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| b15 | b14 | b13 | b12 | b11 | b10 | b9 | b8 | b7 | b6 | b5 | b4 | b3 | b2 | b1 | b0 | ||
| Gate-Array | Write only | 0 | 1 | - | - | - | - | - | - | - | - | - | - | - | - | - | - |
| RAM Configuration | Write only | 0 | - | - | - | - | - | - | - | - | - | - | - | - | - | - | - |
| CRTC | Read/Write | - | 0 | - | - | - | - | r1 | r0 | - | - | - | - | - | - | - | - |
| ROM select | Write only | - | - | 0 | - | - | - | - | - | - | - | - | - | - | - | - | - |
| Printer port | Write only | - | - | - | 0 | - | - | - | - | - | - | - | - | - | - | - | - |
| 8255 PPI | Read/Write | - | - | - | - | 0 | - | r1 | r0 | - | - | - | - | - | - | - | - |
| Expansion Peripherals | Read/Write | - | - | - | - | - | 0 | x | x | x | x | x | x | x | x | x | x |
Legend:
- "-" means this bit is ignored,
- "0" means the bit must be set to "0" for the hardware device to respond,
- "1" means the bit must be set to "1" for the hardware device to respond.
- "r1" and "r0" mean a bit used to define a register
Official I/O Ports
The official ports are defined to eliminate conflict between devices, as follows:
| I/O | Decoded as | Port | Read | Write |
|---|---|---|---|---|
| #7FXX | %01xxxxxx xxxxxxxx | Gate Array | - | Write |
| #7FXX | %0xxxxxxx xxxxxxxx | PAL extension to Gate Array for 128K RAM banking | - | Write |
| #BCXX | %x0xxxx00 xxxxxxxx | 6845 CRTC Index | - | Write |
| #BDXX | %x0xxxx01 xxxxxxxx | 6845 CRTC Data Out | - | Write |
| #BEXX | %x0xxxx10 xxxxxxxx | 6845 CRTC Status (as far as supported) | Read | - |
| #BFXX | %x0xxxx11 xxxxxxxx | 6845 CRTC Data In (as far as supported) | Read | - |
| #DFXX | %xx0xxxxx xxxxxxxx | Upper ROM Bank Number | - | Write |
| #EFXX | %xxx0xxxx xxxxxxxx | Printer Port | - | Write |
| #F4XX | %xxxx0x00 xxxxxxxx | 8255 PPI Port A (PSG Data) | Read | Write |
| #F5XX | %xxxx0x01 xxxxxxxx | 8255 PPI Port B (Vsync,PrnBusy,Tape,etc.) | Read | - |
| #F6XX | %xxxx0x10 xxxxxxxx | 8255 PPI Port C (KeybRow,Tape,PSG Control) | - | Write |
| #F7XX | %xxxx0x11 xxxxxxxx | 8255 PPI Control-Register | - | Write |
| #F8FF | N/A | Peripheral Soft Reset (MC_BOOT_PROGRAM and MC_START_PROGRAM do OUT [F8FF],FF) | - | Write |
| #FA7E | %xxxxx0x0 0xxxxxxx | Floppy Motor Control (for 765 FDC) | - | Write |
| #FADC | %xxxxx0x0 xx0xxx00 | Amstrad Serial Interface Z80-SIO / DART port A Data Register | Read | Write |
| #FADD | %xxxxx0x0 xx0xxx01 | Amstrad Serial Interface Z80-SIO / DART port A Control Reg. | Read | Write |
| #FADE | %xxxxx0x0 xx0xxx10 | Amstrad Serial Interface Z80-SIO / DART port B Data Register | Read | Write |
| #FADF | %xxxxx0x0 xx0xxx11 | Amstrad Serial Interface Z80-SIO / DART port B Control Reg. | Read | Write |
| #FB7E | %xxxxx0x1 0xxxxxx0 | 765 FDC (internal) Status Register | Read | - |
| #FB7F | %xxxxx0x1 0xxxxxx1 | 765 FDC (internal) Data Register | Read | Write |
| #FBDC | %xxxxx0x1 xx0xxx00 | Amstrad Serial Interface 8253 Timer counter 0 | Read | Write |
| #FBDD | %xxxxx0x1 xx0xxx01 | Amstrad Serial Interface 8253 Timer counter 1 | Read | Write |
| #FBDE | %xxxxx0x1 xx0xxx10 | Amstrad Serial Interface 8253 Timer counter 2 | Read | Write |
| #FBDF | %xxxxx0x1 xx0xxx11 | Amstrad Serial Interface 8253 Timer Modus Select | - | Write |
- The three 765 FDC floppy ports are contained in CPC 664/6128/Plus and DDI-1 only.
- The eight Amstrad Serial Interface ports are pre-defined as shown above in the AMSDOS ROM. However, neither the CPC 664/6128/Plus nor DDI-1 do actually contain the corresponding RS232 hardware.
- Bit14 of the PAL selection address must be at 1 on CPCs equipped with CRTCs 0/1/2. It can be at 0 or 1 on CRTCs 3/4. For compatibility reasons, it is strongly advised to always set bit14 to 1 to select PAL.
- As components use partial address decoding, it is therefore possible to send the same value to different components simultaneously by carefully using custom I/O ports.
Memory Mapped I/O Ports
| Mem | Decoded as | Port | Read | Write |
|---|---|---|---|---|
| #4000-7FFF | %01xxxxxx xxxxxxxx | ASIC - CPC+/GX4000 registers | Read | Write |
See the ASIC page for details.
