Re: Software for MS-DOS 1.25

From: Michał Pleban <lists_at_michau.name>
Date: Sat, 21 Oct 2017 06:01:03 +0200
Message-ID: <59EAC67F.2040908@michau.name>
Mia Magnusson wrote:

> Well, AFAIK you can't REP more than one instruction. The question is
> will the 8088 throw away the result of one CMP when the next one runs
> in the REP loop? Or is it possible to break out of the REP loop if CMP
> sets the condition codes to "the data differs"?

Right. It would probably be necessary to do something like this:

loop:
CMPSW
JNE ...
LOOP loop

> Maybe the improved board could be an add-on to another Commodore 8-bit
> machine. For example the 8296 has faster memory than it actually needs
> as it in one 1MHz half cycle does two fetches for the video hardware.
> That would mean that with a reprogrammed PLA the CPU could use the
> memory at 2MHz :)

There is a 6809 card for the 8296 but I think it runs at 1 MHz?
Something similar could be done here, but running an 8088 at 1 MHz does
not look promising. The 8296 and CBM-II have very different hardware
architecture.

Regards,
Michau.




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Received on 2017-10-21 05:00:02

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