Questions tagged [mos-6526]

Questions about the MOS 6526 CIA (Complex Interface Adapter) chip, used in e.g. the Commodore 64 home computer and the Commodore 1570/1571 floppy drives.

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3
votes
5answers
207 views

What use are the data direction registers in the MOS 6526 CIA?

As described in the MOS 6526 CIA data sheet (at the bottom of page 5) and this answer, the PA0-7 and PB0-7 pins: always act as inputs, even when the data direction register (DDR) is set to 1 ("output"...
5
votes
1answer
280 views

Where are the pullups for the Commodore 64 keyboard matrix lines?

I'm looking at the schematic and the Service Manual for the Commodore 64. I can't seem to find a schematic for the keyboard itself. It seems clear that the control port 1 joystick has normally open ...
17
votes
2answers
671 views

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 ...