The Amstrad CPC firmware manual was for sale back then, but it's freely available now: http://www.cantrell.org.uk/david/tech/cpc/cpc-firmware/ http://www.cantre

The Amstrad CPC firmware manual was for sale back then, but it's freely available now: http://www.cantrell.org.uk/david/tech/cpc/cpc-firmware/ http://www.cantrell.org.uk/david/tech/cpc/cpc-firmware/ In particular, there's the following note about TXT UNWRITE in the Indirections section: "This routine works by comparing the image on the screen with the character matrices; therefore if the character matrices have been altered the routine may not find a readable a character"