I'd say it looks as much like firmware as a
PROM implemented as a
of diodes, some of which have been cut. :-)
So, Wang Laboratories made a series of machines it called the
100-series. There were display (Nixie tube) and printing versions of
The logic of the machine was small-scale DTL/TTL IC's.
It was a microcoded architecture.
The microcode sequencer consisted of a TI TMS 2600 ROM, which took
inputs from various state flip flops, and generated control signals that
ran the microcode through the sequences. The microcode itself
was...wait for it...
Two large circuit boards populated with diodes! The microcode itself
was "hard wired' in diodes.
Please don't murder me. I was young and foolish... I have the remains of
one of those somewhere :-(
I got it yeras ago, and used the keyboard, case, and PSU as part of my
first homebrew machine. I think i have the main PCBs mostly intact still.
I did desolder some of the connectors and maybe tghe odd IC, though.
IIRC there wewre 3 boards in the pile. The bottome 2 were the didoe
matrix firmware ROMs, the top one was full of mostly TTL. Ther was
anoitehr 24 pin IC (the ROM you mention) and some RAMs (1101a?). I seem
to rememebr a coupele of smalelr PCBs tht fitted on top, display drivers?
The machine was developed at a time that MOS ROM wasn't quite there in
terms of size and cost to hold the microcode, so the diode ROM was used.
Question is: Is the diode ROM "firmware"?
I would say the diodes and PCB are hardware, in the same way that an EPOM
chip is hardware. The (electrical)_ layout of the diodes is firmware.