My #Commodore #CBM8032 has very likely a broken 6520 PIA. The SRQ line does not work, which is not tragic, since it is not used. But I want to pass the diagnostic test. Since I have plenty 6821 and it is a #PIA, too and it is pin compatible and the registers also look the same, I gave it a try and installed on in my PET #CBM3016. It is socketed there 🙂 I have tested it a lot and it seems, that it works.

Yesterday, I have run a demo on my original hardware #Commodore #CBM3016 #PET, that made me really wonder. It displayed some hires graphics, although there in no such thing on the computer. This has let me do some schematics reading and consulting „The PET Revealed“. It is about a carefully timed modification of the screen RAM, referenced to the vertical sync. I am deeply impressed.