> 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 > battery.
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). -tony > > --Chuck > > >
