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Old 1st Mar 2021, 7:19 pm   #732
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,485
Default Re: Non-working Commodore PET 3016

Doesn't seem to be anything wrong with UD2, which is producing the UD6 _CS1 (pin 20) pulse that you are showing on your yellow upper trace.

With power on, can you check the voltage on UD6 CS3 (pin 21)? (should be +5V).

When you are looking at UD6 pin 11 (D2) you are also looking at UD7 pin 7, UD8 pin 11, and UD9 pin 11 because all of those pins are connected together.

The fact that you have no activity on the D2 data line when UD6 _CS1 is low is surprising. As I recall, you just about got your Arduino Mega PROM reader working. If it's still lying around, try reading UD6 to see if it is still OK.
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