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Boards from a 3270 PC

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mcs_5

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Dec 21, 2019
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I have the boards from an IBM 3270 PC (type 5271). The mainboard has a lot of bodge wires. Reading the Byte review, it's hinted that the mainboard may not be completely standard.

https://archive.org/stream/byte-mag...09-09_Guide_to_the_IBM_PCs#page/n237/mode/2up

Are all these bodge wires standard? Is it a standard 5160 mainboard?

I got these boards, when I bought the PC chassis from a scrap dealer many years ago (early 90s). I just bought the chassis and PSU - and the boards came along... Back then I had no idea what all the strange boards were. I just removed them, and have had them since :)

3270-8.jpg

3270-9.jpg
 
I am not surprised it has "bodge wires" as it was pretty much thrown together and had the odd operating system that can run DOS programs alongside the 3270 emulation program, and its likely that mods were needed to get this to work. It was only ever available as a custom unit. You could not order the bits to convert an ordinary PC to a PC3270. In fact you will also find such fixes on many IBM cards.
 
Is the operating system special? I thought is was just standard DOS, with a 3270 TSR. That's the way 5250 terminal software works (for S/36, AS/400 etc). I've worked with those a lot, but never 3270 stuff until it was just software and TCP/IP ;)

I'm not sure I ever tested the motherboard. I guess I should do that... I remember testing the video card, and getting no output. But I probably didn't have the keyboard card installed, so the video card had no BIOS. I also don't know what monitor is correct for this card. I probably had an EGA monitor back then.

Should I replace the 15 orange firecrackers before powering up the board?
 
Here are the "special" cards from the system. The video card is three boards sandwiched together. The centre board can be used on it's own, and the other two add graphics support and custom character set support (if my research is correct).

The small board converts the keyboard from AT to XT protocol, adds timing circuits and the BIOS for the video card.

The single full-length board is the "host connect" board.

3270-1.jpg

3270-2.jpg

3270-3.jpg

3270-5.jpg

3270-6.jpg

3270-7.jpg

There must have been a floppy controller as well. But perhaps I used that elsewhere sometime during the last 25+ years ;)
 
also, I've been working on putting one together and have everything now except the main board if you don't have a need for it
 
Al Kossow said:
It would be nice if you could dump the BIOS if you have a way to do that
Click to expand...

There are three of them ;)

The two chips on the mainboard are a TMM23256P, which has the standard 27C256 pinout, and a MK37050-4, which has the 27C64 pinout. So my EPROM programmer should be able to read those.

The BIOS chip on the keyboard card is a ceramic package EPROM, but I can only read the date code and "JAPAN" without removing the label...
 
Al Kossow said:
also, I've been working on putting one together and have everything now except the main board if you don't have a need for it
Click to expand...

I don't need a "special" XT mainboard, if it actually is special. Perhaps the BIOS contents can reveal something...
 
mcs_5 said:
Is the operating system special? I thought is was just standard DOS, with a 3270 TSR. That's the way 5250 terminal software works (for S/36, AS/400 etc). I've worked with those a lot, but never 3270 stuff until it was just software and TCP/IP ;)

I'm not sure I ever tested the motherboard. I guess I should do that... I remember testing the video card, and getting no output. But I probably didn't have the keyboard card installed, so the video card had no BIOS. I also don't know what monitor is correct for this card. I probably had an EGA monitor back then.

Should I replace the 15 orange firecrackers before powering up the board?
Click to expand...

The software is what differentiates the 3270PC from a PC with a 3270 card. Its really a sort of multitasking hypervisor. More details here:-

https://en.wikipedia.org/wiki/IBM_3270_PC

if you have a graphics display it ma be you have a 3270PC/G which used a different base unit.....
 
I've dumped the ROMs, at least. The Motorola chip on the keyboard card is likely to be a microcontroller, but without the use of fuming nitric acid I'm not sure how you'd prove it.

I'm not aware of IBM releasing any technical documentation for the 3270PC (unlike the PC, XT or AT). Maybe they didn't want to give away information about the 3270 terminals the PC was based on.
 
Last edited:
g4ugm said:
if you have a graphics display it ma be you have a 3270PC/G which used a different base unit.....
Click to expand...

The graphics board was also available as an upgrade. There's a manual with installation instructions at Bitsavers.
 
I may have found the keyboard from this system. It could also by a keyboard from a 5250 terminal. I'm not familiar enough with these to tell the difference... The label on the bottom is not very informative.

Terminal_kb.jpg

Terminal_kb2.jpg

Terminal_kb3.jpg

Terminal_kb4.jpg

I also have a dca IRMAkey/3270 keyboard, that should have the correct layout. But I have no idea if that uses the same scancodes as IBM's keyboards. It's electrically compatible at least.
 
Thats a 5250 keyboard. Not sure if the scan codes map, probably not. 3270 keyboards have the keys labeled PF1 thru PF24 have PA1, PA2 and PA3 keys above the cursor , and have a second enter on the numeric pad... ... Sorry...
 
mcs_5 said:
Yes, that's the question. Different key caps only, or different firmware as well...
Click to expand...

I suspect different firmware. The 3270 keyboard always had separate scan codes for PF keys. I think on a 5250 there was a "CMD" key so you did "CMD" the a "1" for CMD1 (I think) and I suspect that one may generates two scan codes for the CMD keys. I know getting good CMD key mapping using an XT keyboard with a "£" sign was a royal PIA ...

.... if the connector fits all you can do is try it...
 
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