IBM 3270 interfacing?

[Mike Ross]

Date: Sat, 13 Nov 2004 11:13:53 +0100
From: Tore S Bekkedal <toresbe at ifi.uio.no>
Subject: IBM 3270 interfacing?
To: cctech at classiccmp.org

>Does anyone know anything about the protocol that the IBM 3270 terminals
>uses on the BNC ports labelled I/O? Is there any possibility of hooking
>this up to anything modern?

3270 terminals use... 3270 protocol, at the lower levels, to send noises 
down a coax wire. At the higher levels, you get into heavy-duty blue-glue 
acronyms you don't want to touch with a condom-covered bargepole. Like BSC, 
SNA... <shivers>.

Here's the trick. These 3270 terminals hook up, not directly to hosts (well, 
except for a few special cases), but to terminal controllers. The least 
ancient of these are type 3174 - search ebay for IBM 3174* and you'll find a 
few usually. 3174-2x are best. Pay $10-$50 perhaps.

These normally hook up directly to mainframes, via bus/tag channels or 
escon, or remotely to mainframes, via modems and wierd IBM protocols. You 
want nothing to do with either.

The 3174s also came with options for token ring (pretty cheap now) and 
ethernet (still ruinously expensive) attachment. Get one of those, and get 
the latest version of the controller microcode (C6.4 I think) from IBM. This 
magic microcode allows you to also use the 3174 as a telnet client - you 
boot the controller, power on any coax-attached 3270 terminals - and the 
terminal displays a screen which essentially allows you to type 'telnet 
<hostname>' and connect, like any other telnet client or serial terminal 
(but with a funky keyboard!).

See http://www.corestore.org/emuterm.htm for some my adventures with this 
stuff!

Mike
http://www.corestore.org