
Building an IBM 3270 terminal controller - rbanffy
https://ajk.me/building-an-ibm-3270-terminal-controller
======
kev009
I have actual 3174s with FICON attach for my 9377 and z800. Also have a
Memorex-Telex 3174 clone. They are interesting machines in themselves. It's
appropriate to think of a mainframe as a distributed system of sorts, where
these controllers are distinct systems that participate with the mainframe CPU
over channel I/O and offload most of the terminal handling functionality.

~~~
rbanffy
The other day I made the analogy that a mainframe looks a lot like a cluster
of specialized ludicrously fast machines attached to a ludicrously fast
network.

------
dhosek
The IBM mainframe architecture was such that the mainframe didn't deal with
individual keypresses at the terminal, instead interactions were bundled at
the terminal and sent a record (which could be a whole screen full of XEDIT
work) at a time. This meant that normally only IBM terminals could be used,
but it was possible to use a dedicated system for managing dumb ASCII
terminals to translate to EBCDIC and emulate a lot of the computational power
of the 3270 terminals.

~~~
lowobservable
Yep, the IBM 3174 terminal controller Asynchronous Emulation Adapter or
feature allowed you to connect ASCII terminals to a mainframe host and allowed
3270 devices to connect to an ASCII host. There were options from other
companies in those days too.

Later, with LAN connectivity, there was quite a bit of bridging different
technologies you could do with a 3174.

------
qubex
This is wonderful. I have a bunch of 5250-type terminals left over from IBM
S/38 and AS/400 systems and I’ve been wanting to find a way of using them as
VT-100 devices as TTYs for use with Linux _& cetera_ since forever.

Is there any chance that this might come next?

~~~
rbanffy
Shouldn't be impossible - they are somewhat similar to 3270's. Unfortunately,
there isn't a Hercules for the AS/400\. Someone would need to create it.

~~~
qubex
Frankly I’d be super-content if I could just use one of my old terminals as a
TTY for a Unix machine, even perhaps something as humble as a Raspberry Pi.

~~~
lowobservable
The National Semiconductor DP8344 datasheet has some details on the Twinax
interface and the 5250 terminal architecture as it was a later IC that
supported both 5250 and 3270. I've not read the Twinax part in detail bit
skimmed over it; it looks like an extension of the 3270 concept.

The topic has come up on Cctalk mailing list (see
[http://classiccmp.org/pipermail/cctalk/2019-November/051008....](http://classiccmp.org/pipermail/cctalk/2019-November/051008.html)),
and I think Alan was looking to build what you are talking about but was
looking for some help reverse-engineering the higher-level protocol.

------
zxcvbn4038
Awesome project! It would be fun to hook one of these up to a raspberry pi
running Hercules. Nostalgia factor would be epic.

~~~
lowobservable
I wish there were more terminals available. Unfortunately some of the more
exciting models like the 3279 (a cool wedge shaped color model) and 3290
(large orange plasma screen) seem to be practically unavailable.

Also lots of the earlier terminals got separated from their keyboards :(

~~~
blackbit
I do have a 3290 on my desk. There are two kinds of 3270 terminals, CUT and
DFT. The 3290 is of the variant that is currently not supported by oec.

------
_sbrk
I remember the days of 3270 terminals and, later, x3270 under SunOS & Solaris
to the university VM.

