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.
Questions tagged [mos-6526]
4 questions
6
votes
5 answers
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") for that pin, and
the outputs are open drain,…
cjs
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