Text scrolling error in Mode 7

bbc micro/electron/atom/risc os coding queries and routines
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fuzzel
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Joined: Sun Jan 02, 2005 1:16 pm
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Text scrolling error in Mode 7

Post by fuzzel » Wed Nov 27, 2019 2:34 pm

While writing my text adventure I've encountered a fairly unusual error. When the text / inputs hit the bottom of the screen, instead of scrolling down the text / inputs start again at the top of the screen, overwriting what was written there previously. All I've done is to add some more objects to my list which utilises another block of RAM (&B00), previously my list was stored at &900 and &A00. Any obvious reason why this is happening?
I could restore a backup from a couple of days ago but I'd rather understand what I may have done wrong.

fuzzel
Posts: 651
Joined: Sun Jan 02, 2005 1:16 pm
Location: Cullercoats, North Tyneside
Contact:

Re: Text scrolling error in Mode 7

Post by fuzzel » Wed Nov 27, 2019 3:48 pm

I think I've found the answer to my own error. By increasing the number of objects by one I accidentally also changed the end of a loop which had the same value as the number of objects. This ended up changing a zero page address around &D0 which seemed to changed the scrolling.

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