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Update apple2_hires.md

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tilleul 2021-01-15 09:55:34 +01:00 committed by GitHub
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@ -22,7 +22,7 @@ So to draw the entire line 0 we could `RUN` this code
POKE 8232,255
will not plot 7 pixels on line 1 but on line 64 !
If we slightly modify the above code to POKE the first 3 lines in memory, we have
If we slightly modify the above code to POKE the first 3 lines as stored in memory, we have
10 HGR
20 A = 8192: REM $2000
@ -34,5 +34,10 @@ If we slightly modify the above code to POKE the first 3 lines in memory, we hav
80 PRINT A
The result is this
![screenshot](img/apple2_hires_lines0-64-128.png)
We have drawn line 0, line 64 and line 128 !
Now the next address to `POKE` seems to be 8312 ($2078 in hex -- the resulting value in our variable `A`).
But if we do `POKE 8312, 255` we don't see any change on the screen ! This is because we have reached one the hires screen holes !
In fact, all lines between 128 and 191 in RAM have 8 unused bytes at their end. Those 8x64 lines represent 512 bytes. Those are the missing bytes in first computation.