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A comment on The Amstrad CPC 472, an unusual case. Parent comment

Re:The Amstrad CPC 472, an unusual case by seanwilson on Tuesday September 15, 2020 @08:21AM (#24480375)
Cool, that's a pretty weird/neat hack. How come you know about how it was implemented?
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Re:The Amstrad CPC 472, an unusual case by unnah on Tuesday September 15, 2020 @09:53AM (#24481188)
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/

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"

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