Quote:
Originally Posted by Slothie
The 6522 is a completely different chip. The 6522 has 16 registers, the 6520/21 only 4. The pinout is different. The 6520 and 6521 are equivelents however.
The PET has 6520's and a 6522 for the user port.
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Thanks for the more detailed info.
Yes, I did say the 6522 was a kind of 'enhanced' 6520 - and do recall the 16 registers from my Beeb-Programming days. But I wondered if 4 of these were the same as those on the 6520 (being as it seems the INS8154 PIA can be replaced with 6522, as share they same registers, even if H/W needs changing)
Just looking at the pinouts for the 6520 & 6522, it seems most pins are the same, but 6pins have changed function.
With A0-A1 (for 4 registers) becoming RS0-RS3 (for 16 registers) - but on different pin-positions, although could be re-mapped.
However, main issue might be CS0 (if used) is no longer on 6522 and there's only one nIRQ rather than 6520's nIRQA & nIRQB.
6521's don't seem to be that common, but 6821's should be (I'm sure I've got some, and believe I used one on a project at Uni back in the 90's)