CPC Guide - Input/Output port addressessValid I/O Port addressess
PORT

&7Fxx   Gate array
&BCxx   CRTC: select register
&BDxx   CRTC: register data 
&BFxx   CRTC: data

&DFxx   Expansion rom select
&EFxx   Centronics data

&F4xx   8255: port A data (PSG)
&F5xx   8255: port B data (Cassette, Printer, Misc sensing)
&F6xx   8255: port C data (PSG,Keyboard scanning,Cassette)
&F7xx   8255: control

&F8xx   Expansion Bus
&F9xx   Expansion Bus
&FAxx   Expansion Bus

&FA7E   FDC: Disk drive motor control

&FBxx   Expansion Bus

&FB7E   FDC: main status register
&FB7F   FDC: data register

&FFxx   NOT USED

&FADC   Serial: SIO Channel A data
&FADD   Serial: SIO Channel A Control
&FADE   Serial: SIO Channel B data
&FADF   Serial: SIO Channel B control
&FBDC   Serial: 8253 Load Counter 0
&FBDD   Serial: 8253 Load Counter 1
&FBDE   Serial: 8253 Load Counter 2
&FBDF   Serial: 8253 Write Mode Word



For those port addressess in the expansion bus range: Ports &F8xx to &FBxx xx 
byte as specified below: 
&00 - &7B       DO NOT USE
&7C - &7F       Disc Interface
&80 - &BB       DO NOT USE
&BC - &BF       Reserved for future use
&C0 - &DB       DO NOT USE
&DC - &DF       For  communications interfaces
&E0 - &FE       Available for user expansion interfaces
&FF             Bus Reset interfaces