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Forums > C64 Coding > Black background when sideborder open
2018-09-15 00:38
Golara

Registered: Jan 2018
Posts: 98
Black background when sideborder open

I've got this effect where I open almost the whole sideborder to show a "raster bar" go by the screen. Everything was working like normal until I replaced my macro loops with proper code generators. The effect is still working, but I've got a black background.


When you look at the normal view it looks like the sideborder is still closed but there's a sprite on top of it.



Any ideas ?
 
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2018-09-16 00:09
Raistlin

Registered: Mar 2007
Posts: 129
Judging from the screenshot, that just looks like they're changing $3fff on each rasterline. The value will repeat across the line and then be read again at HSYNC for the next line.
2018-09-16 00:20
Oswald

Registered: Apr 2002
Posts: 4316
krill, cool workaround didnt think of that so far :D what I did sometimes is simply change ffff back and forth sometimes you can have that irq outside the display area.
2018-09-16 06:40
ChristopherJam

Registered: Aug 2004
Posts: 868
Quoting Compyx
I always thought that was $F9FF ?

It is. EBCM zeros the address lines that would ordinarily select which quarter of a charset VIC is accessing, so in this instance it just shifts the ghost byte down from the end of the bank by 1536 bytes (3/4 of the 2k a charset occupies).
2018-09-16 08:07
Krill

Registered: Apr 2002
Posts: 1095
Yes, $F9FF. Sorry, brainfart. :)
2018-09-16 08:11
Krill

Registered: Apr 2002
Posts: 1095
Quoting Raistlin
Judging from the screenshot, that just looks like they're changing $3fff on each rasterline. The value will repeat across the line and then be read again at HSYNC for the next line.
It's read continually, actually. Changing the visible pattern mid-line is possible, so you can have $3FFF-splits. :)
2018-09-16 09:24
oziphantom

Registered: Oct 2014
Posts: 240
with an REU you can change it per char to make a "picture"
2018-09-17 14:07
Perplex

Registered: Feb 2009
Posts: 216
Quoting Krill
Yes, $F9FF. Sorry, brainfart. :)


A shame it's not $FAFF, that would be the perfect address for the idle byte.
2018-09-17 14:52
Golara

Registered: Jan 2018
Posts: 98
Quote: Quoting Krill
Yes, $F9FF. Sorry, brainfart. :)


A shame it's not $FAFF, that would be the perfect address for the idle byte.


why ?
2018-09-17 14:58
Krill

Registered: Apr 2002
Posts: 1095
Wiktionary and Urban Dictionary are your friends. :)
2018-09-18 08:01
Firehawk

Registered: Aug 2011
Posts: 29
@oziphantom: Yes, check out the QI demo where James did some exellent raster/3fff images.
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