Epson MX-80 Technical Manual?
ard.p850ug1 at gmail.com
Wed Nov 9 23:19:32 CST 2016
> IIRC, the MX-80 had serial (RS232) as an option with Centronics
> standard. The interesting thing was that the only thing the option
> really gave you was the EIA-to-TTL level shifting logic. I recall
> cobbling an adapter up using a couple of 2N2222 transistors and a 9V
These Epson printers (not just the MX80, but other somewhat related models)
had a header socket on the logic board that carried the Centronics signals
and a few other things. It was designed for custom interface boards.
One such board was indeed a bit-banged (by the printer's microcontroller)
RS232 interface. There was a pin on the connector that you grounded to
get the microcontroller to read in bit-banged data. I think the Centronics
data lines were used to read a DIP switch on the interface board to
specify things like baud rate.
Other intefaces used the Centronics interface in a more conventional
way. There was an RS232 board with its own microcontroller and
buffer RAM that didn't use the bit-banging functions of the printer
microcontroller. There was an IEEE-488 interface from Epsom (it
was a load of TTL from what I recall). And HP made an HPIL
interface board to go there (microcontroller and 1LB3 chip).
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