On the other
hand, there was the 6551 ACIA emulation in software for
the user port, which was buggy to boot. People may make fun of the Plus=
/4
but at least it had a real ACIA.
They did? (Looking in handy box of manuals, but plus 4 isn't in there..=
.)
Yes, accroding to my Plus4 service manual, it's location U3 on the main
PCB. It's a real 6551, not even part of some other I/O chip. The serial
port pins are buffered to TTL levels and brought out on he user port
connector as you might expect.
-tony