Ok, I'm a little bored, and al ittle high, so here's the PROM simulator
story. I was working on a device that had a(n?) 80186, which controlled
the video on a 9" monitor, and the company's claim to fame was the "bend
board" - we'd write a pixel pattern of a waveform, but then there was a
special little circuit that would introduce a little magnetic deflection
between pixels, to get rid of the pixellations and produce a trace that
looked like a long-persistence analog EKG, like you see on TV. This was
a 4-channel "remote heart-rate monitor", used in hospitals, where the
patients were ambulatory, but still needed to be monitored. They'd carry
around a little transmitter, about the size of two packs of cigarettes,
with 5 or so leads plugged into it with EKG stickers stuck all on their
chest, in the prescribed spots. It was a little transmitter, of the EKG
signal, using some really cheap technology like five V/F bands in the
audio range. Anyway, the unit I worked on had four receivers, for
four channels, so they could monitor four patients. The software
(firmware?) took the four analog signals which had been ADC'd, and did
some digital filtering on them, and showed the patient's EKG on this
monitor.
So, anyway, I was hired as "programmer", I think, although I think the
fact that I'd been a tech might have played in there. What my coworker
and I did was maintain and improve the firmware for this 80186 that ran
this display device - four parallel digital filters, display drivers, bend
board drivers, a strip chart recorder - but that's the "8048 FIFO" story -
and we'd make a mod to the program, burn a pair of EPROMs, slap them in
the test system and test it. Everybody's heard that one, haven't they!
Edit, compile, burn, plug, crash. Edit, compile, burn, plug, crash. Edit,
compile, burn, plug, run! Hooray! ;-)
So, we ascertained that it would be cheaper in the long run to go ahead
and make a ROM simulator, where we could bypass the erase/burn cycle, and
it's just be edit, compile, load, run/crash. ;-)
So, I slapped together a little design with a couple of 6116s and LS245s
and stuff, that looked like a PROM to the DUT and like a memory block to
the host PC.
Well, I was all set to go ahead and prototype it up myself, but one of
the guys who outranked me said, "Just give it to the production people -
they'll have one for you by this afternoon."
Well, does anyone remember those schematics in the early magazines and
stuff, where they show all of the bypass capacitors on a bus, and just
"Vcc" and "Gnd" labels at the chips? This board was wire-wrapped
impeccably - yea, verily, perfectly - to my schematic. The assembler had
put all of my bypass capacitors right next to each other on busses right
at the power entry point to the board. Each chip had Vcc and Gnd, of
course, but EEk! I really had to restrain myself and be all patient and
stuff as I 'splained to the assembler, "Oh, gosh, I'm sorry, I only drew
them that way to indicate that they're _electrically_ in parallel, there
was supposed to be one per chip..."
And, not necessarily surprisingly, she immediately understood the point I
was trying to make, and while she was redoing the wiring I redrew the
schematic with all of the damn lines drawn to all of the damn chips and
all of the damn bypass capacitors right next to their damn chips; but it
worked like a champ!
Cheers!
Rich
