IBM 5251 terminal USB conversion (but not what you think)

listofoptions

02 Oct 2020, 02:13

thats cool, ive found some; let me know if these work, im planning on spinning up my own to do some data-sniffing around a system 32/34/36/38 i have occasional access to.
here are my notes for the 5250 anyway:

connector for panel mount connector Amphenol 082-5590-RFX
cable ends use Amphenol 082-5589-RFX
use Belden 9207 or equivalent

the cable ends and connectors should be 50-ohm (93ohm are hens teeth) and the cable is 100ohm (also a hens tooth, but Ive seen 100, 107, 93, 78, etc.. for twin-ax characteristic impedance ratings, so YMMV apparently)

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inmbolmie

02 Oct 2020, 08:24

listofoptions wrote:
02 Oct 2020, 02:13
thats cool, ive found some; let me know if these work, im planning on spinning up my own to do some data-sniffing around a system 32/34/36/38 i have occasional access to.
here are my notes for the 5250 anyway:

connector for panel mount connector Amphenol 082-5590-RFX
cable ends use Amphenol 082-5589-RFX
use Belden 9207 or equivalent

the cable ends and connectors should be 50-ohm (93ohm are hens teeth) and the cable is 100ohm (also a hens tooth, but Ive seen 100, 107, 93, 78, etc.. for twin-ax characteristic impedance ratings, so YMMV apparently)

Connectors look fine. Cable in theory is 110Ω but yes, for short cables it shoudn't be that important. For some time was operating with a random twisted pair cable and terminators on a prototype board and worked just the same. Obviously if you run long cables with multiple stuff connected that becomes important.

monty11ez

12 Dec 2020, 04:44

This is so amazing. I was just looking for a nice terminal project for my computer and came across some IBM terminals that looked really nice, but I didn't know how to connect them to a modern computer. Fortunately Google brought me here, so it looks like I might have a new project on my hands.

Pingmeide

05 Jan 2021, 20:27

Hi, I just want to report that the 5250 adapter I got from Inmbolmie in July still works very well. The IBM 3477 Terminal I obtained works fine with the box and I use the terminal frequently - the picture quality is far more friendly (crisp) for the eyes than the normal computer screen.(In my opinion) Back in mid-2020 inmbolmie was very helpful in creating a "mapping" table for the German keyboard-layout and the money I spent was a good investment - thanks again !

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inmbolmie

Yesterday, 00:23

Pingmeide wrote:
05 Jan 2021, 20:27
Hi, I just want to report that the 5250 adapter I got from Inmbolmie in July still works very well. The IBM 3477 Terminal I obtained works fine with the box and I use the terminal frequently - the picture quality is far more friendly (crisp) for the eyes than the normal computer screen.(In my opinion) Back in mid-2020 inmbolmie was very helpful in creating a "mapping" table for the German keyboard-layout and the money I spent was a good investment - thanks again !
You are welcome, I'm happy that the converter worked well for you.

I have a couple of updates for this project. I recently got a new scope and was finally able to capture the signals over the wire, so here they are to document how the converter works at that level.

First, some frames from the converter. Yellow is Channel-A, blue is Channel-B, and purple is A minus B

Spoiler:
DS1Z_QuickPrint33.png
DS1Z_QuickPrint33.png (54.77 KiB) Viewed 78 times
DS1Z_QuickPrint34.png
DS1Z_QuickPrint34.png (54.59 KiB) Viewed 78 times
The same capture for frames generated by the 5251 as a comparison

Spoiler:
DS1Z_QuickPrint35.png
DS1Z_QuickPrint35.png (48.47 KiB) Viewed 78 times
DS1Z_QuickPrint36.png
DS1Z_QuickPrint36.png (44.05 KiB) Viewed 78 times
The captures were made with the line fully terminated. You can see levels are a little higher and transitions a little overshot in the converter signal, but nothing terrible and they are better than I expected. Also maybe the 5251 signal is a little smoothed because it was sampled at the other end of the cable.

Capture showing both, request and response

Spoiler:
DS1Z_QuickPrint37.png
DS1Z_QuickPrint37.png (61.72 KiB) Viewed 78 times

The second update is about performance, some time ago the Python script performance was quite improved compared to what was published here, so I include a second video showing some more ASCII action as a comparison. I show Asciiquarium, text scrolling and the very famous ASCII Star Wars movie.


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