The 82143A consists of a printer and an HP-41 interface module permanently linked by a seven conductor cable. It uses a three-wire clocked bidirectional synchronous protocol, similar to National Semiconductor's Microwire. A Motorola 3270 (single-chip micro based on the Fairchild F8) in the printer controls the transfer.
I opened the 82143A to get at the signals, and wired the PIC up as a passive observer. This has the disadvantage that I get the printed output whether I want it or not. If I knew what the other three signals were doing I might try to disconnect the entire printer box and use only the 41C module and cable. (Inside the printer end the cable does plug into the PCB with a seven-pin connector.)
This hack would have actually been useful back in the days before HP-IL. Of course, there weren't CMOS PICs with EPROM or EEPROM program memory back then, so I probably would have had to use a 6805 instead.
Last updated January 16, 1995
Copyright 1996 Eric Smith