| [[CRTC]] || Read/Write || - || 0 || - || - || - || - || r1 || r0 || - || - || - || - || - || - || - || -
|-
| [[Upper ROM Bank Number|Upper ROM select]] || Write only || - || - || 0 || - || - || - || - || - || - || - || - || - || - || - || - || -
|-
| [[Printer Port]] || Write only || - || - || - || 0 || - || - || - || - || - || - || - || - || - || - || - || -
|-
|}
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.