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.
I/O Port Mapping
| Hardware device | Address | Read/Write | b15 | b14 | b13 | b12 | b11 | b10 | b9 | b8 | b7 | b6 | b5 | b4 | b3 | b2 | b1 | b0 |
| Gate Array | &7F | Write Only | 0 | 1 | - | - | - | - | - | - | - | - | - | - | - | - | - | - |
| PAL | &7F | Write Only | 0 | - | - | - | - | - | - | - | - | - | - | - | - | - | - | - |
| CRTC Select | &BC | Write Only | - | 0 | - | - | - | - | 0 | 0 | - | - | - | - | - | - | - | - |
| CRTC Write | &BD | Write Only | - | 0 | - | - | - | - | 0 | 1 | - | - | - | - | - | - | - | - |
| CRTC Status | &BE | Read Only | - | 0 | - | - | - | - | 1 | 0 | - | - | - | - | - | - | - | - |
| CRTC Read | &BF | Read Only | - | 0 | - | - | - | - | 1 | 1 | - | - | - | - | - | - | - | - |
| ROM select | &DF | Write Only | - | - | 0 | - | - | - | - | - | - | - | - | - | - | - | - | - |
| Printer port | &EF | Write Only | - | - | - | 0 | - | - | - | - | - | - | - | - | - | - | - | - |
| PPI Port A | &F4 | Read/Write | - | - | - | - | 0 | - | 0 | 0 | - | - | - | - | - | - | - | - |
| PPI Port B | &F5 | Read/Write | - | - | - | - | 0 | - | 0 | 1 | - | - | - | - | - | - | - | - |
| PPI Port C | &F6 | Read/Write | - | - | - | - | 0 | - | 1 | 0 | - | - | - | - | - | - | - | - |
| PPI Control | &F7 | Write Only | - | - | - | - | 0 | - | 1 | 1 | - | - | - | - | - | - | - | - |
| FDC Status | &FB | Read Only | - | - | - | - | - | 0 | - | 1 | 0 | - | - | - | - | - | - | 0 |
| FDC Data | &FB | Read/Write | - | - | - | - | - | 0 | - | 1 | 0 | - | - | - | - | - | - | 1 |
| FDC Motor | &FA | Write Only | - | - | - | - | - | 0 | - | 0 | 0 | - | - | - | - | - | - | - |
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, - means this bit is ignored.
I/O Ports
| 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.
Memory Mapped I/O Ports
| Mem | Decoded as | Port | Read | Write |
| #4000-7FFF | %01xxxxxx xxxxxxxx | ASIC - CPC+/GX4000 registers | Read | Write |