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Old 26th Feb 2021, 6:00 pm   #683
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 7,318
Default Re: Non-working Commodore PET 3016

Originally Posted by Mark1960 View Post
There is also my misunderstanding of the chip select behaviour on the PET. I expected a separate chip select pulse for each memory access, but thats not the case.
Actually, I think it is as you understood it to be. Although there are two chip selects on each PROM, the active high CS3 is tied directly to +5V so the only one being used is the active low _CS1 (pin 20).

The relevant diagram section is:-

Or in case you are having trouble viewing that, here's a screen grab.
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