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 PIO Port A (PSG Data) Read Write
#F5XX %xxxx0x01 xxxxxxxx 8255 PIO Port B (Vsync,PrnBusy,Tape,etc.) Read -
#F6XX %xxxx0x10 xxxxxxxx 8255 PIO Port C (KeybRow,Tape,PSG Control) - Write
#F7XX %xxxx0x11 xxxxxxxx 8255 PIO 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 ? Amstrad Serial Interface Z80-SIO / DART port A Data Register Read Write
#FADD ? Amstrad Serial Interface Z80-SIO / DART port A Control Reg. Read Write
#FADE ? Amstrad Serial Interface Z80-SIO / DART port B Data Register Read Write
#FADF ? 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 ? Amstrad Serial Interface 8253 Timer counter 0 Read Write
#FBDD ? Amstrad Serial Interface 8253 Timer counter 1 Read Write
#FBDE ? Amstrad Serial Interface 8253 Timer counter 2 Read Write
#FBDF ? 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