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 [[I/O Port Summary|Complete I/O Port Summary]].
== I/O Ports ==<br>
{|{{Prettytable|width: 700px; font-size: 2em;}}|'''== I/OPort Allocation Rules == Components use partial address decoding. It is therefore possible to send the same value to different components '''||'''Decoded assimultaneously'''by carefully using custom I/O ports. {|class="wikitable"! rowspan=2|Hardware device !! rowspan=2|Read/Write !! colspan=16|'''Port'''bits|-! b15 !! b14 !! b13 !! b12 !! b11 !! b10 !! b9 !! b8 !! b7 !! b6 !! b5 !! b4 !! b3 !! b2 !! b1 !! b0|-| [[Gate Array]] || Write only || 0 || 1 || - || - || - || - || - || - || - || - || - || - || - || - || - || -|-| [[PAL16L8|PAL]] (RAM configuration) || Write only || 0 || * || - || - || - || - || - || - || - || - || - || - || - || - || - || -|-| [[CRTC]] ||'''Read'''/Write || - || 0 || - || - || - || - || r1 || r0 || - || - || - || - || - || - || - || -|-| [[Upper ROM Bank Number|Upper ROM select]] ||'''Write''' only || - || - || 0 || - || - || - || - || - || - || - || - || - || - || - || - || -|-| [[Printer Port]] || Write only || - || - || - || 0 || - || - || - || - || - || - || - || - || - || - || - || -|-| [[8255|8255 PPI]] || Read/Write || - || - || - || - || 0 || - || r1 || r0 || - || - || - || - || - || - || - || -|-| Expansion Peripherals || Read/Write || - || - || - || - || - || 0 || x || x || x || x || x || x || x || x || x || x|} Legend:*"-" means this bit is ignored,*"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.*"r1" and "r0" mean a bit used to define a register* "*" Bit14 of the PAL port 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. <br> == Official I/O Ports == The official ports are defined to eliminate conflict between devices, as follows: {| class="wikitable"!I/O!Decoded as!Port!Read!Write
|-
|#7FXX||%01xxxxxx xxxxxxxx||[[Gate Array]]||-||Write
|-
|#7FXX||%0xxxxxxx xxxxxxxx||[[PAL16L8|PAL ]] extension to [[Gate Array]] for 128K RAM banking||-||Write
|-
|#BCXX||%x0xxxx00 xxxxxxxx||6845 [[CRTC]] Index|| - ||Write
|#EFXX||%xxx0xxxx xxxxxxxx||[[Printer Port]]|| - ||Write
|-
|#F4XX||%xxxx0x00 xxxxxxxx||[[8255]] PIO PPI Port A ([[PSG]] Data)||Read||Write
|-
|#F5XX||%xxxx0x01 xxxxxxxx||[[8255]] PIO PPI Port B (Vsync,[[Printer Port|PrnBusy]],Tape,etc.)||Read|| -
|-
|#F6XX||%xxxx0x10 xxxxxxxx||[[8255]] PIO PPI Port C (KeybRow,Tape,[[PSG]] Control)|| - ||Write
|-
|#F7XX||%xxxx0x11 xxxxxxxx||[[8255]] PIO 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 FDC is considered as an expansion peripheral. 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 ==<br>
== Memory Mapped I/O == {|{{Prettytable|width: 700px; font-size: 2em;}}class="wikitable"|'''!Mem'''||'''!Decoded as'''||'''!Port'''||'''!Read'''||'''!Write'''
|-
|#4000-7FFF||%01xxxxxx xxxxxxxx||[[ASIC]] - CPC+/GX4000 registers|| Read || Write
|-
|}
Writes to unused areas of the ASIC I/O page are not persisted. [https://www.cpcwiki.eu/forum/games/harrier-attack-reloaded/msg247703/#msg247703 Source]
See the [[ASIC]] page for details.
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[[Category:Programming]] [[Category:CPC Internal Components]]