25 Nov
2007
25 Nov
'07
11:17 p.m.
As there is no 3270 coax card and no open slot to have
once held one,
I suspect that the 3270 host interface is the unknown card in slot 7.
I own IBM SDLC and Bisync adapter cards, and this one doesn't look
like either.
Physical characteristics:
* 8-bit, short card.
* One DB25F on the bulkhead.
* 9x Oki M37S64-20; apparently 64Kx1 memories.
THose aren't piggybacked chips by any chance, are they?
* 34 pin .100" header, vertically, at back end of
card (J2)
* one 4-pos DIP switch at top right.
* Pretty much everything else on the card is 74LS-series TTL or passive.
It's built like IBM made it, but I can't find any obvious IBM-style
part number on it, unless it's 2683541. Google is silent on this
number. (update: I just noticed 6320999 in the etch, but that hasn't
gotten me any closer to an answer).
I know of one card that almost matches that description, except that
there are puggybacked RAMs for a total of 128K. Ans that's a combined
parallel printer card and 128K RAM card (together with 256K on the
motherboard and 256K on the memory card, that would give you the 640K
maximum RAM of a PC/XT system).
I have one here. It says 'PN 6236193' in the silkscreen on the solder
side of the PCB, and has '6236194' in the etch. Otherwise it matches your
description, except that U27 is a delay line (you didn't mention one of
these)
I thought the 3270 host interface was a full-legth card with a BNC socket
on the brakcet and an 8X300-seires microcontroller on it. But I might be
thinking of soemthing else.
-tony