Added the 6551 UART and I’m almost able to talk to this over serial if it wasn’t for baud rate problems. I’m blaming the 1.8432 MHz UART clock, it isn’t the canned oscillator variety so prone to noise or some such? Who knows?
The 1.8432 MHz clock is required by the 6551’s internal baud rate generator, but there’s an option to bypass this internal baud rate generator and set the baud directly off a clock signal.
Looking at the 6551’s datasheet and I should be able to get something out of it, albeit at a crazy baud rate, if I set bit 4 of the control register to 0 and feed it the 1MHz CPU clock, which I know is good.