Re: visual 6502 simulation...

From: Ethan Dicks <>
Date: Thu, 16 Sep 2010 12:14:28 -0400
Message-ID: <>
On 9/16/10, Rhialto <> wrote:
> On Thu 16 Sep 2010 at 10:38:30 +0200, "André Fachat" wrote:
>> I voted for the 6522 as next chip to analyze, to find out about the
>> shift register bug.
> Speaking of shift register bugs: there is this one that I don't remember
> being explained. If you enable sound on a PET, then try to load anything
> from cassette, the PET hangs. The STOP key does not work, nor does
> anything actually load.

Yes.  I remember that one (especially since a lot of my early work was
fiddling with CB2 sound and I didn't own a disk drive).

> See
> which also notes "NOTE: Location 59467 must be reset to zero for
> cassette to function properly". But that shift register isn't used for
> cassette loading, right?

It's not, but ISTR some vague stories about putting the shift register
into free-running mode (which is how one gets sound) triggers some
hidden problem.  I'd love to know what is _really_ going on in there
(not that we could fix the problem).

I'm suddenly curious if the 65C22 has the same issue (I have a few of
each; I should try it).


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Received on 2010-09-16 17:00:31

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