MIT provides MULTICS source and documentation (DPS-8 simulation)
ard at p850ug1.demon.co.uk
Thu Nov 15 15:11:52 CST 2007
> > 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=
> > 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.
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