Re: 5251/Twin-Ax terminal emulation

I’ve got a few of those; I’ve got MCA, PCMCIA, ISA and PCI ones. My experience with those is downright horrible though, except for the MCA one. The USB->Twinax adapter is really nice though. In the end, I either use that one, or an InfoWindow II 3489.

One thing OP might find interesting about the TwinData USB adapter is that it can be abused to sniff a twinax bus on a higher level. If you give it the same ID as an existing terminal you can use it to eg capture the password on a QDSIGNON screen. Internally it uses a FTDI USB UART chip, so you can use your standard software-based serial port sniffing tools to analyse the protocol with it as well. It’s been a great tool to troubleshoot flaky connections.

/y

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________________________________
From: MIDRANGE-L <midrange-l-bounces@xxxxxxxxxxxxxxxxxx> on behalf of Jason Olson <josys36@xxxxxxxxx>
Sent: Tuesday, December 3, 2019 5:27:34 PM
To: Midrange Systems Technical Discussion <midrange-l@xxxxxxxxxxxxxxxxxx>
Subject: Re: 5251/Twin-Ax terminal emulation

Personally I don't know why you would go through all this effort. It's
pretty easy to pick up some 5250 ISA and PCI cards off eBay, and connect to
an older system that way. I still have a few terminals at home that I use,
but I also have a 5250 PCMCIA card in my IBM T60 Thinkpad that I use the
most. I was able to grab 4 of these off eBay about 10 years ago.

So besides the technical hey I did this kinda thing, what are you trying to
accomplish here?


Thanks,

Jason E. Olson
IBM i Engineer/Developer
josys36@xxxxxxxxx
480.223.2952


On Mon, Dec 2, 2019 at 9:33 AM <alan@xxxxxxxxxxx> wrote:

All,

I've built a line-sniffer for my mid-80s System/36 (5362) in an attempt
to fully understand the TwinAx electrical and protocol layers. The long
term goal is to build an affordable open-source terminal emulator
providing either a TN5250 bridge to emulated TwinAx terminal sessions or
a more simple telnet/ASCII/vt10x translation on a series of TCP ports by
a WiFi ESP32. twindata.com offers a lot of similar products but they
are closed-source and far outside of the price range of most retro
computing enthusiasts. There doesn't appear to be a lot of people
running older System/32, S/34, S/38 and gen-1 AS/400s. But the keyboard
pirates are slowly destroying older terminals and I want the surviving
machines to be easy to interface to so they can be as usable as
possible.

I've worked through all the electrical and framing issues and annotated
a few dumps of the S/36 IPL with both an InfoWindow II and 3179
attached. The output of which can be found here:

https://www.retrotronics.org/tmp/s36_ipl_decodes1_01dec19.zip

The message structure and limited command descriptions came from this
document starting on PDF page 122 / printed page number 4-9:


http://bitsavers.trailing-edge.com/pdf/ibm/5250_5251/SY31-0461-0_5251_Display_Station_Model_11_Maintenance_Information_Dec77.pdf


However it is incomplete. Not all commands are enumerated, the modifier
address bits are not explained (addresses a LU inside the terminal), and
none of the context or arguments for the commands are elaborated on. A
simple example of what I am referring to is, for example, the
explanation of the argument bits for the SET MODE command, etc.

Can anyone point me to a document or resource that fully explains the
TwinAx 5251 model 12 display protocol? I've been searching for days now
and no luck. And I really can't make anymore progress until I'm
unblocked by documentation. I simply don't have enough time to
trial-and-error reverse engineer bit meanings.

Thanks,

Alan Hightower
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