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RS-232 "breakout boxes" for serial connection troubleshooting

Terry Kennedy

Experienced Member
Joined
Jul 7, 2017
Messages
241
Location
New York
It looks like we don't have a topic for these yet, so I created this one. Feel free to post any information you have regarding specific models, tips and techniques as applied to interfacing vintage computers, modems, and terminals.
 
I'll start off with a link to my blog entry on the Datatran Datatracker series of breakout boxes. Earlier this month I sent scans of the DT-5 manual to bitsavers and it is now available there. I created my blog entry to go into more (some would probably say excruciating :rolleyes:) detail about these devices, as well as posting a higher-resolution version of the manual.
 
That DT-5 does look like a nice box! I like that it has turret terminals instead of pins you never have enough jumpers for :) I've got the little "poke 24 AWG phone wire into it" types scattered around, as you say in your blog post, they're fine for simple problems. I've ordered a DT-4 to check out.

I'm a big fan of the IQ Technologies SmartCable SC821 Plus. They're still available but pretty expensive new, you can pick them up used for around $20-25. The nice thing about the SC821 Plus is that you can rapidly try a bunch of common combinations using slide switches, and tie up handshake lines using DIP switches. It's not quite as versatile as a plugboard style breakout box: you can't leave stuff completely disconnected as easily, which sometimes matters. For instance, the Intel SDK-80 will smoke a resistor if you just plug onto it with a full-wire DB25 or DB25 to DE9, due to having non RS-232 signals on the connector.

Here's the SC821 Plus in action:

hWAw6ND.jpg
 
My stock of DB-25 breakout boxes dates from the early 80s. One used to see boxes filled with the things at computer fairs and swap meets. My needs basically settle down to an LED box for monitoring line status and a bunch of "jumper" boxes for various tasks such as "null modem" etc.

They were very inexpensive and did the job.
 
My stock of DB-25 breakout boxes dates from the early 80s. One used to see boxes filled with the things at computer fairs and swap meets. My needs basically settle down to an LED box for monitoring line status and a bunch of "jumper" boxes for various tasks such as "null modem" etc.

They were very inexpensive and did the job.

Yeah, I don't think I've ever bought one of the plugboard style retail, just they end up in lots of equipment or in the $1 box at hamfests! Christmas tree lights boxes too.
 
Is that device restricted to RS232 levels or can it also function with RS422/RS485?

Just 9 pin interface? What do you do when there's also reverse-channel signaling?
 
My goto is an old BlackBox model that I found in a junk bin at work:

BlackBox Bobcat - BlackBox Bobcat breakout box

Watching a printer manipulate the signals is kind of fun. I recently made a video of an IBM Compact Printer doing it's thing through the breakout box: https://youtu.be/bI5eb7tRA0U

(Yes, I'm mesmerized by blinky lights ...)
 
Heh, looks just like the DT-5 from Terry's blog post, except black plastic. I bet BlackBox OEMed it!
 
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