Re: LDA C08C,X

[Doug Kwan <NOSPAMdkwan@gauge.transmeta.com>]

Bryan Parkoff <BParkoff@satx.rr.com> wrote:
:     Please explain what LDA C08C,X is.  I know that it is read mode into
: byte latch.  Please look below:

: C65E: BD 8C C0 LDA C08C,X

: C661: 10 FB BPL C65E {-05}

: C663: 49 D5 EOR #D5

:     It requires to loop until bit is high.  Does it mean that it has to loop
: 8 times until 8 bits are filled in a byte latch?  Is it possible to add "STA
: 4000" between LDA and BPL so I can see one bit out of 8 bits into one byte
: storage?  Why do EOR #D5 have to be used instead of CMP like AA and 96.
:     I do have Beneath Apple DOS/ProDOS manual in front of me, but it does
: not provide me enough information.  It is why I am asking a question in
: newsgroups so someone might be able to provide more information.  I
: appreciate this.

EOR does not change the carry bit in the status register but CMP does.
RWTS uses the carry flag to signify error in many places. That may be the
reason.

-Doug

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