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| From: Marko_Mäkelä
Date: 2000-07-25
Subject: Re: Interrupts
|
On Tue, 25 Jul 2000, Pigmy wrote:
> > Eg: ASL $FF09 - clears the requests, besides it is working like:
> > read $FF09, eg.:$82 (irq request), then shift left: $04, and write
> > back.
Read-modify-write instructions write the unmodified value back first. So,
the ASL $ff09 will first write $82, then $04.
> As I remember, only those bits are cleared in $FF09 which are set in
> the value. E.g.: $FF09 contains $12 and you put $10, then it will
> contain $02... Am I right?
That's the way it works on the VIC-I, VIC-II and VIC-IIe video chips.
Probably that's the way also on the TED; I don't remember.
Marko
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