(This thread might be better in "Programming".)
This has answered something I must have mused about on and off for years and years and years! Can you switch in any memory area to display as the screen memory...mmm...maybe....what about...perhaps not...on the other hand...
And there it is, staring me in the face on p. 370 of the Advanced User Guide for the last 41 years! "The ability to define the start of the screen to be anywhere in memory is very useful..." !
My immediate use for this would be to have up to 20 or maybe 25 different Teletext frames (ie. mode 7 screens) in memory at once and switch to them by re-programming the CRTC, but there's a complication with mode 7. The formula on p.372 to convert the memory address into the 6845 R12 and R13 values doesn't work (especially as I get a negative number after the first subtraction). If I fill a 1K block of memory (say at &2000) with &FFs, nothing I've tried has turned that into the mode 7 screen, but it does work in the other modes.
This has answered something I must have mused about on and off for years and years and years! Can you switch in any memory area to display as the screen memory...mmm...maybe....what about...perhaps not...on the other hand...
And there it is, staring me in the face on p. 370 of the Advanced User Guide for the last 41 years! "The ability to define the start of the screen to be anywhere in memory is very useful..." !
My immediate use for this would be to have up to 20 or maybe 25 different Teletext frames (ie. mode 7 screens) in memory at once and switch to them by re-programming the CRTC, but there's a complication with mode 7. The formula on p.372 to convert the memory address into the 6845 R12 and R13 values doesn't work (especially as I get a negative number after the first subtraction). If I fill a 1K block of memory (say at &2000) with &FFs, nothing I've tried has turned that into the mode 7 screen, but it does work in the other modes.
Statistics: Posted by BeebMaster — Mon Sep 09, 2024 10:19 pm