Author
| why is the msx reading from 0xAA (PPI port C)
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flok
msx novice
Posts: 25 |  Posted: August 06 2008, 01:37 |
Hi,
I wonder: why is the MSX constantly reading from port 0xAA (PPI port C)?
From the documentation I found this is either a write only port or it returns the last written value.
In both cases: why on earth is it bothering?
Folkert.
-- www.vanheusden.com/msx-emul/ |
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NYYRIKKI
msx master
Posts: 1528 | Posted: August 06 2008, 02:27 |
Because the keyboard read routine goes like this:
IN A,(#AA)
AND #F0
OR <row to read>
OUT (#AA),A
IN A,(#A9)
... you just don't want to change Caps lamp, click status etc. when you read keyboard.
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flok
msx novice
Posts: 25 | Posted: August 06 2008, 12:34 |
ah ok
thanks!
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