Port $80 is used to send a value to select a register. Port $81 is for associated data; both support reading and writing. Similar to the operation of integrated circuits such as the PSG or a VDP, it allows sending many values with a minimal interface.
[[File:bM0V3i.png|200px|thumb|left|4colour game PCWplus]]
This is how '''KachorroSoft''' created the incredible colour ports of '''AMC''' and '''MadMixGame''' with graphics from the CPC; '''Phantis''' from MS-DOS CGA and CPC; and '''Hundra''' from the ZX Spectrum. But with new colour palettes.
[[File:bM0V3i.png|200px|thumb|left|4colour game PCWplus]]
[[File:+Z1d33.png|200px|thumb|left|loading screen PCWplus]]
[[File:69KUrt.jpg|200px|thumb|right|4colour game PCWplus]]