{|{{Prettytable|width: 700px; font-size: 2em;}}
|'''I/O'''||'''Decoded as'''||'''Port'''||'''Read'''||'''Write'''
|-
|#1C00||%x0xxxx00 xxxxxxxx||[[Dk'tronics Lightpen]] faulty mirror of #BCXX [[CRTC]] Index|| - ||Write
|-
|#1F00||%x0xxxx11 xxxxxxxx||[[Dk'tronics Lightpen]] faulty mirror of #BFXX [[CRTC]] Data In|| Read || -
|-
|#78XX||?||[[CPC4MB|4Mb Memory extension]]||-||Write