Questions tagged [mos-6522]

Questions about the MOS 6522 VIA (Versatile Interface Adapter) chip, used in e.g. the Commodore PET and the BBC Micro home computers.

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2 votes
1 answer

What is the advantage of using CB2 over CA2 on the PET user port?

According to schematic 320130-1 (from the user port on the PET brings out from the 6522 PIA all data lines from port A (PA0-PA7), the port A input-only handshaking line (CA1), and the ...
3 votes
1 answer

Does the 6522 VIA swap the registers for ports A and B compared to the 6820 PIA and 6526 CIA?

According to this preliminary datasheet and what appears to be a later CSG data sheet from some data handbook, the 6522 VIA assigns to registers 0 through 4, DR (data register) B, DR A, DDR (data ...
6 votes
2 answers

Why did the Vic-20 need special chips for I/O?

The Vic-20 used two 6522 VIA chips for I/O. I asked why it had two of them but thanks to a comment from Bruce Abbott, I now think that wasn't quite the question I needed to ask. What I really need to ...
6 votes
3 answers

What is the difference between the 6522 VIA and a UART?

The 6522 VIA is an I/O chip used in the Vic-20. I was under the impression that UART (Universal Asynchronous Receiver/Transmitter) is the general term for such chips, so was surprised to see this: ...
5 votes
1 answer

Why does the Vic-20 have two VIA chips?

The Vic-20 uses the 6522 VIA for peripheral I/O. However, it has two of them. I find this surprising, particularly considering minimizing cost was an important design goal. Is there a reason why it ...
10 votes
1 answer

Could the Commodore 64 have used the 6522 VIA instead of the 6526 CIA?

The VIC-20 used a 6522 VIA chip with a couple of 8-bit PIO ports, a couple of timers and a (buggy) shift register. (The bug in the shift register could be worked around with external hardware or in ...
18 votes
2 answers

Comprehensive test suites for MOS 6520 PIA / 6522 VIA / 6526 CIA

Are there any automated test suites for MOS 6520, 6522 and 6526 chips? I am looking for test suites aimed at making sure datasheet-based independent reimplementations of the above chips (e.g. FPGAs or ...