Re: Interesting C64/6526 case

From: groepaz_at_gmx.net
Date: Fri, 26 Oct 2018 15:58:17 +0200
Message-ID: <5336594.Wdh5Q80WDE@rakete>
Am Freitag, 26. Oktober 2018, 15:52:51 CEST schrieb silverdr@wfmh.org.pl:
> > On 2018-10-26, at 15:48, silverdr@wfmh.org.pl wrote:
> > 
> > Now, we know those cases when the characters are garbled (not like garbage
> > character but the character definitions are wrong). If not the CHAROM and
> > not the CIA
> s/CIA/PLA/
> 
> I meant PLA, of course...
> 
> > then the next goto chip is the U2 CIA. Checking the bits on its Port A is
> > often enough to find that the lines read wrong combination, effectively
> > preventing VIC from accessing the CHAROM. Now to the interesting case.
> > I've got a CIA that passes all the diagnostic tests, including both
> > ports. Moreover works all well everywhere (C64 U1, 1571) as long as it is
> > not the U2 position in C64. There it causes the garbled characters
> > symptom. Anyone willing to take a stab at possible explanation?

i'd measure if it actually manages to pull down the bank select lines

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Received on 2018-10-26 16:02:46

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