 Previous Messages |
Posted By
siz
on 2024-10-12
09:16:15
|  Re: Raster interupt 9th bit
Ah, so I can't fully draw in the whole top border?
Of course you can. Just a bit tricky.
The raster counter starts at line 0 (obviously) at line 4/8 starts the screen (25/24 rows mode) and ends at line 199/203 (24/25 rows mode) bottom border ends at line 250/226 (PAL/NTSC) then vertical retrace and top border starts at line 275/248 (PAL/NTSC) and goes to 311/261 (PAL/NTSC) and rolls over to 0.
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Posted By
Crown
on 2024-10-11
13:05:20
| Re: Raster interupt 9th bit
"invalid" rasterlines should not trigger interrupts normally, unless you override the raster counter with illegal values, ie writing something bigger then 0x138 into $ff1c-$ff1d. In this case the wrap will happen after 0x1ff, and illegal compare value should trigger raster interrupt when matched.
This is something to verify, but it should work like this.
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Posted By
Fuzzweed
on 2024-10-11
12:22:59
| Re: Raster interupt 9th bit
"starts 4 rasterlines above the usable area of a 25 column screen"
Ah, so I can't fully draw in the whole top border?
I'll check my code before I post  . I think I'm just loading #$00 into the compare register but could be something stupid like missing #
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Posted By
siz
on 2024-10-11
11:23:52
| Re: Raster interupt 9th bit
Logically id thought b0,$00 would be the very first line but it doesn't seem like that in practice (actually it seems that starts below the top border)
It starts 4 rasterlines above the usable area of a 25 column screen.
Do you know how it interprets an 'illegal' compare such as $x1,$FF?
Any "invalid" rasterlines (anything above 311 for PAL and 262 for NTSC systems) does not trigger a raster interrupt.
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Posted By
SukkoPera
on 2024-10-11
09:06:45
| Re: Raster interupt 9th bit
Please post the code you are using.
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Posted By
Fuzzweed
on 2024-10-11
08:40:20
| Re: Raster interupt 9th bit
Ok thankyou. If is logical then it is probably a problem with my code
Do you know how it interprets an 'illegal' compare such as $x1,$FF?
Ignores it? Or some logical interpretation of lsb?
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Posted By
gerliczer
on 2024-10-11
06:13:56
| Re: Raster interupt 9th bit
How is the 9th bit of the raster interrupt related to the raster line?
Completely naturally. It is the MSb of the raster line counter. The counter counts from 0 to 311 or 261 then wraps.
Logically id thought b0,$00 would be the very first line but it doesn't seem like that in practice (actually it seems that starts below the top border)
It is right above the display area. That is the logic here, that's what you will have to adapt to.
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Posted By
Fuzzweed
on 2024-10-11
04:02:23
| Raster interupt 9th bit
How is the 9th bit of the raster interrupt related to the raster line?
Logically id thought b0,$00 would be the very first line but it doesn't seem like that in practice (actually it seems that starts below the top border)
So if b1,$00 is very top left (?) how does the main 8bit register work. Just b1,$00-$38? Or b1,$00-FF but it overlaps with b0,$00-$FF.
I hope that makes sense, I'm slightly confused.....
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