Default I/O Port Summary
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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 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.
- 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.