Interesting C64/6526 case

From: silverdr_at_wfmh.org.pl
Date: Fri, 26 Oct 2018 15:48:24 +0200
Message-Id: <920BA810-C9CE-4E0A-803E-8600308CFB86@wfmh.org.pl>
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 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?

-- 
SD! - http://e4aws.silverdr.com/
Received on 2018-10-26 16:00:02

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