I guess I could read the analog port as the square wave changes from the PMW and react based on that?
I had planned on using https://www.jameco.com/z/6551-Major-Brands-IC-6551-Asynchronous-Communication-Interface-Adapter-DIP-28-pin_43318.html since it's from Jameco when I order more parts for various things.
I think, and I may be very wrong, the ACIA needs a phi2 input (1-2MHz) to actually put a byte into its internal bus from a computer on D0-D7, then it is transferred between ACIAs via the actual baud rate on the serial transmit pin. Not entirely sure about this, though.