HP 82143A to RS-232 interface

I recently needed to dump the HP 82143A microcode for use with my HP-41 simulator. The only simple means I have of doing so is to use the disassemble command of the MCED function in the ZENROM. Unfortunately the disassembler can only output to a printer, or a device which the HP-41 can otherwise be convinced is a printer, such as an HP 82164A HP-IL/RS-232 converter. Since the HP-41 can only have one printer interface plugged in at a time, and I didn't want to manually type in 12288 hex digits from a roll of thermal paper, I programmed a PIC to convert the synchronous serial protocol used internally in the 82143A to standard RS-232 asynchronous serial.

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.

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Last updated January 16, 1995

Copyright 1996 Eric Smith