[Coco] CoCo 3 MMU test for all
flexser at fiu.edu
Mon Jan 21 17:50:25 EST 2008
You might want to check whether your assembler assembled LDB 0,X and LDB ,X
using the same postbyte for both, if both gave you $38. I'm pretty sure
LDB 0,X, if assembled correctly, should have yielded $78, same as PEEK does.
On Mon, 21 Jan 2008, Robert Gault wrote:
> Arthur Flexser wrote:
> > Roger, the value you get from reading an MMU address depends on exactly HOW you
> > read it, I discovered some years back. This arose when I noticed that the value
> > I got from PEEK differed from the value returned by the MON function in ADOS (ML
> > monitor). I traced this to the fact that PEEK used something like LDA 0,X while
> > MON used LDA ,X. The different postbyte affected whether I got $7x (PEEK) vs.
> > $3x (MON). So, I think asking people to PEEK an MMU address and report the
> > results will give you a somewhat misleading impression.
> > Art
> That's interesting. I just tried a test with EDTASM ZBUG with the
> following code.
> start lda $ffa0
> ldx #$ffa0
> ldb 0,x or as an alternate ldb ,x
> Ran the code and examined the register contents. Both regA and regB were
> $38. However, a PEEK(&HFFA0) from Basic gives $78.
> Your on to something Art, but I'm not sure what.
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