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Computek PCM210 - what is this ISA card?

ppieczul

Experienced Member
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Jun 20, 2018
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51
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Poland
Hi,
In one of the old 286s I found the Computek PCM210 card.
It uses only power from the ISA slot and has two connectors: DB9 and RC.
It has NEC8506 CPU on it and EPROM.
Seems like a microcontroller thing - any idea what this might actually do and why in a PC?
Thanks
Pawel
IMG_0089.jpg
 
Can't be. Look at the lack of fingers on the ISA connector--and no memory on board. The 40-pin NEC chip, I believe, is an MCU. Beyond that, I have no idea what this might be used for.
 
No RAM so likely not a video card of any type.

Very minimal microcontroller so could be most anything and Computek is a fairly common corporate name so no direction there. One Computek did sell high end graphics equipment but this does not look like those. The few fingers on the card edge mean it has to have very limited communication with the main system.

Any idea on what it came from? My guess would be something like a serial port network for use with POS systems. But just a guess.
 
Definitely not a video card per se. IOW, you can't plug it into a monitor and get it to display on that monitor.

Maybe some sort of converter.
 
Yeah, it's a puzzle. You wouldn't use an MCU of that vintage to do video conversion; not RS232 either, as there aren't any EIA transceivers. Looks like it exists mostly to suck power from the bus. Could be an interface for a printer sheet feeder or some such, but that's just a wild guess.
 
There is a German thread here from 2015 having the same conversation

https://forum.classic-computing.org/forum/index.php?thread/8402-computek-pcm-210/

From using Google Translate, it looks like something for a POS system was mentioned then too. It does fit the mold of POS hardware - oddball, not documented, uses a microcontroller + an EPROM rather than a custom chip so likely limited production run.

Possibly this could have been a controller for a VFD 'pole display' device? It's the only part of a POS system I can think of that wouldn't be directly compatible with a standard interface; the employee's display would just be a standard monitor (an awful lot of 9" monochrome CGA and VGA displays were made for POS use), keyboards (even if designed for POS) would just use the standard keyboard interface, barcode scanners would be serial or 'keyboard wedge' types, receipt printers would be serial or parallel. Cash drawers usually plug into the receipt printer, and networking surely would have been easier and cheaper to do with Ethernet or some other off the shelf system rather than designing special hardware?
 
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The onboard crystal has an association to DTMF codes, so maybe a card to interpret phone key presses and convert them to numbers?
 
I was thinking the network would be similar to one of the derivatives of ZX Lan but I may be deceived by the combination of 9-pin and simple plug with planned space for a second plug so a more complex version of the card could daisy chain the network.
 
Thanks for the answers and the link to the forum.
This is definitely not monitor connector, there seems to be power on the CGA GND pin and plugging monitor causes immediately a short circuit.
The RCA is connected through a resistor to the emitter of a pnp transistor.
The ISA is used only for power: +5V -5V (used only for collector of that pnp transistor) and GND. No communication with the motherboard.
I found it in Commodore PC30-III system.
It is intriguing. I think I will try to read the eprom and look for some strings, unfortunately it is not in a socket.
 
A big clue here is in the ISA connector... notice no interface pins whatsoever? It's a completely passive card - it involves the host PC in no way whatsoever. It just takes in the 5V (VCC) and GND lines, all on the back (B-side) of the card. It takes in GND, VCC, and -5V for some reason, but that's it - no I/O logic at all.

You can at least guarantee there's no software that goes along with it (since it only uses the PC for power) - and that the EPROM chip is for the microcontroller's use, not the PC.

Wonder if the RCA jack is an audio output - resistor, transistor before it... well, if it's audio, it'd probably be a capacitor isolating it. Hmm. Yeah, still a bit lost.

Can we get a photo of the back side of the board?
 
Here you go. When I find some time I will dump the ROM and see with oscilloscope what is at the RCA.
It seems like MCS 48 type of microcontroller, we should be able to disassembly it or maybe even emulate.
IMG_1285.jpg
 
That XTAL is 3.57954 MHz, which is colorburst frequency for NTSC.
So, while it's obviously not a graphics card, perhaps it does generate some video signal? Like some test pattern?
 
That XTAL is 3.57954 MHz, which is colorburst frequency for NTSC.
So, while it's obviously not a graphics card, perhaps it does generate some video signal? Like some test pattern?

I doubt it--the crystal was probably chosen because it was an item manufactured in large quantities and therefore, inexpensive.
 
With the transistor on the RCA jack, I'd say it was an output to a buzzer.
The 8039 would have a hard time doing anything with color so using it as a color video generator would be a real stretch. Especially since the ports are wired directly to the 9 pin connector. It might be interesting to see how the I/O pins are configured. My guess is that it is to monitor something and buzz if there is an issue, It looks like there are 7 or 8 signal from the 9 pin connector that make their way to the 8039. Since, as Chuck says, the crystal was likely selected because it was cheap. The 8039 didn't have internal ROM. I forget which pin it is but one of the pins, set to 0 or 1 ( I forget ) will make it always select the external ROM. During the early days, one could buy parts that had bad 8049 mask but were otherwise OK as processors, these were marked as 8039s. Also 8049 overruns were also marked as 8039s.
Dwight
 
It looks like they optimized this thing for low cost (thus the lack of silkscreen; words burned into copper), but at a low production run as well (thus the EPROM). Dang, if only startups thought like that these days ;)

Ugh, I'm so utterly fascinated by this thing! OK, so I dug a bit (er, a lot) with Google-Fu. Since much of the world revolved around magazines at the time (great places for a glimpse into the past!), I started with a search on Google Books, centered between 1/1/1981 and 1/1/1990. I ended up with not much... in fact, not a single mention of "Computek" in all of PC Magazine. So, they weren't much a consumer-facing device, that rules out a consumer device...

I found a reference to a Computek in a number of places - one referenced to a factory in Canada and being a case study in manufacturing (interesting...?), but book snippets were cut too short to make out many details. Another reference was to a Computek in Burlington, MA in the 1981 time period. Interesting... and that led me to a patent from Computek, maybe related, but maybe just a loose end: http://www.freepatentsonline.com/4281393.pdf

Still digging on more Computek info - knowing what they made will definitely lead to knowing what this thing is for :)

edit: okay, Computek in MA dates back to 1977, before the IBM PC was even created that led to the ISA connector this thing uses. Not sure if I'm onto something...
edit: Computek was around 'til 1990. Definitely the right one.
edit edit: my search seems to end at a reference to a "Computek Publisher Four" computer system in 1984, referenced in a fantastically specific way in Microcomputer Market Place only in my Google results snippet as "Product Name: Computek Publisher Four RAM: 96-256k bytes ROM: 16k bytes Operating System(s): CP-M $6500.00". I might just go to the Palo Alto library just to browse and find this reference on paper, haha...

edit^3: Okay, now digging into the board layout itself. I arranged the two photos side-by-side and mirrored the back side so it overlaps the component positions on the front side (easier to flip back and forth to analyze).
Untitled.jpg
That EPROM layout is very strange to me (why would it need a 74 logic chip in such a simple design?). I'm about 100% certain the earlier-linked datasheet is correct. It references this specific chip, and in doing so, it says that the 8039 is used only with external program memory - OK, cool, that's what we've got. But what I don't understand is the odd layout... datasheet says that DB0...DB7 and P20...P23 are used as address inputs to the external memory during a fetch, then (implicit) the DB0...DB7 pins are used as inputs for the resulting data. Strange to use the same pins as both address output and data input... but I don't see any of that happening on the board here. I can't see where the traces go under the MCU, though... maybe they're routed under it, to the extreme left and between the pins there? (they seem to route P10...P17 on the back side)
Untitled2.jpg
 
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