schematic showing UC1 (MOS6532) traces going through more MC3446 to the IEEE488 connector.
https://assets.chaos.social/media_attachments/files/112/478/262/546/042/520/original/6a6dcb92e01f524e.png
Yeah, I think I've had it wrong. The RIOTs seem to be attached mostly to the IEEE488 port, and the 6522 seems to drive the floppy mechanisms.
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