Default I/O Port Summary

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.

Related pages

• Arnold V specs
• Arnold V Specs Revised