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

The ASIC I/O page is defined as follows:

ADDR	SIZE	POR	TYPE	MNEM	USE
4000h	100h	N	R/W		Sprite 0 image data
4100h	100h	N	R/W		Sprite 1 image data
...	...	...	...	...	...
4F00h	100h	N	R/W		Sprite 15 image data
Block unused
6000h	2	N	R/W	X0	Sprite 0 X position
6002h	2	N	R/W	Y0	Sprite 0 Y position
6004h	1	Y	W	M0	Sprite 0 magnification
6005h	3				(unused)
6008h	2	N	R/W	X1	Sprite 1 X position
600Ah	2	N	R/W	Y1	Sprite 1 Y position
600Ch	1	Y	W	M1	Sprite 1 magnification
600Dh	3				(unused)
...	...	...	...	...	...
6078h	2	N	R/W	X15	Sprite 15 X position
607Ah	2	N	R/W	Y15	Sprite 15 Y position
607Ch	1	N	W	M15	Sprite 15 magnification
607Dh	3				(unused)
Block unused
6400h	2	N	R/W		Colour palette, pen 0
6402h	2	N	R/W		Colour palette, pen 1
...	...	...	...	...	...
641Eh	2	N	R/W		Colour palette, pen 15
6420h	2	N	R/W		Colour palette, border
6422h	2	N	R/W		Colour palette, sprite colour 1
6424h	2	N	R/W		Colour palette, sprite colour 2
...	...	...	...	...	...
643Eh	2	N	R/W		Colour palette, sprite colour 15
Block unused
6800h	1	Y	W	PRI	Programmable raster interrupt scan line
6801h	1	Y	W	SPLT	Screen split scan line
6802h	2	N	W	SSA	Screen split secondary start address
6804h	1	Y	W	SSCR	Soft scroll control register
6805h	1	N	W	IVR	Interrupt Vector (Bit 0 set to 1 on reset)
6806h	2				(unused)
6808h	1		R	ADC0	Analogue input channel 0
6809h	1		R	ADC1	Analogue input channel 1
680Ah	1		R	ADC2	Analogue input channel 2
680Bh	1		R	ADC3	Analogue input channel 3
680Ch	1		R	ADC4	Analogue input channel 4
680Dh	1		R	ADC5	Analogue input channel 5
680Eh	1		R	ADC6	Analogue input channel 6
680Fh	1		R	ADC7	Analogue input channel 7
Block unused
6C00h	2	N	W	SAR0	"DMA" channel 0 address pointer
6C02h	1	N	W	PPR0	"DMA" channel 0 pause prescaler
6C03h	1				(unused)
6C04h	2	N	W	SAR1	"DMA" channel 1 address pointer
6C06h	1	N	W	PPR1	"DMA" channel 1 pause prescaler
6C07h	1				(unused)
6C08h	2	N	W	SAR2	"DMA" channel 2 address pointer
6C0Ah	1	N	W	PPR2	"DMA" channel 2 pause prescaler
6C0Bh	4				(unused)
6C0Fh	1	Y	R/W	DCSR	"DMA" control/status register
Block unused

POR column indicates whether a register has power on reset. A "N" indicates that the contents of a register are undefined at power on.

A colour in the palette is coded in 2 bytes:

• For first byte, bit7..4 is blue value, bit3..0 is red value
• For second byte, bit7..4 is ignored, bit3..0 is green value

Sprite magnification is coded in 1 byte:

• bit7..3 is ignored
• bit3..2 is X magnification (00 = not displayed, 01 = x1, 10 = x2, 11 = x4)
• bit1..0 is Y magnification (00 = not displayed, 01 = x1, 10 = x2, 11 = x4)

Internal Links

• Arnold V specs
• Arnold V Specs Revised