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| From: Marko_Mäkelä
Date: 2000-07-25
Subject: Re: Interrupts
|
On Tue, 25 Jul 2000, Zsolt Prievara wrote:
> > Read-modify-write instructions write the unmodified value back first. So,
> > the ASL $ff09 will first write $82, then $04.
>
> This is very interesting. ASL $xxxx is a 6 cycles long instruction. How do
> the
> instuctions work? What happen exactly in the cycles?
> Is there any recipe for the instruction execution?
Read the 64doc file advertised earlier today. :-) The first two cycles of all instructions are the same: fetch from PC and PC+1. ASL $ff09 goes like this, assuming that $ff09 contains $82:
# addr R/W data
1 PC R 0e
2 PC+1 R 09
3 PC+2 R ff
4 ff09 R $82
5 ff09 W $82
6 ff09 W $04
Marko
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