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I have an old MAI DT4315A that my company was going to throw out.

I'd love to get it setup as a terminal for a linux based system or raspberry pi, just for fun. However, I've never completed anything like this before and was wondering if anyone else has, and can push me in the right direction.

Here's what I know so far:

  • Many people have done this project with VT100 systems or similar. However, those use RS232 I believe, and this terminal uses an RJ45. (Not sure if that even matters.)
  • There's someone who's obviously done it but there's no way to contact them to ask questions: https://www.youtube.com/watch?v=XHAECaEK3dc
  • I've found some documentation on the terminal's pin assignment that may help me come up with a wiring solution to the R-Pi's serial connection: http://chiclassiccomp.org/docs/content/computing/MAI/Fibs/N119.txt
  • I think that it's not as simple as just connecting the pins properly, but that the voltage is also a consideration and I might need something inbetween the Pi and the terminal for that.

Are there any 'defacto' projects/blogs I should be looking at to help with this, or sites that someone else may have read that are commonly pointed to?

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    Assuming people who actually know things confirm that you need one, the thing that converts voltages — almost always between 3.3v on one side and 5v on the other for hobby projects — is called a level converter. They’re pretty cheap, and easy to use on a breadboard, just obviously make sure you get the right thing in terms of uni/bi-directionality and number of signals. – Tommy Dec 5 '19 at 15:41
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    Also, in case it helps those who are not electrical novices such as I: comp.terminals.narkive.com/elmFMsJ8/manual-for-mai-dt4315a describes the pin out, seemingly being 5v, consisting of Tx, Rx, DSR, DTR and plenty of ground, and implies the correct baud rate is 9600, with the terminal being capable of emulating a VT100. – Tommy Dec 5 '19 at 15:54
  • Fantastic information Tommy. I really appreciate it. – SysChaos Dec 5 '19 at 17:36
  • You need to check what the RPi:s serial port can absorb.Is it the normal GPIO pins broken out into a DB-9 connector and nothing else ? The GPIO pins is 3.3 V while RS232 can be anywhere between -25 - -3V and +3 - +25 V. What the meaning of of Tommy's talk of a voltage coverter is that the RPi:s (and moderna computer electronics) really isn't voltage tolerant. – Stefan Skoglund Dec 5 '19 at 20:15
  • @StefanSkoglund - I think what I might get would be an RS232 board that mounts on top of the RPi, and has the MAX3232 to do the level shifting. Seen here: pishop.us/product/serial-hat-rs232 – SysChaos Dec 6 '19 at 17:26
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The RJ45 standard just defines which RS232 signal is on which pin of the connector.

If your RPi has a genuine RS232 output interface, you don't need to do any more level shifting because that will have been done already. RS232 signals use both positive and negative signal voltages, unlike almost anything else in modern digital electronics. The RS232 spec allows for any signal voltage between +/-3V and +/-15V (with an absolute maximum of +/-25V). Most computer-based RS232 ports use +/-5V or +/-10V.

Incidentally, one reason old computer power supplies had -12V and -5V outputs was to provide the negative voltages for the RS232 ports, but electronic circuit design has move on a bit since then.

According to the link in the question, your terminal uses VT100 control codes for cursor movement, clearing the screen, etc. But you should be able to prove the hardware part of the link is working just by sending some letters or digits, without worrying about exactly where they appear on the screen!

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  • That first sentence helps more than you can know. I had assumed the RS232 was a specific port type. Now it makes more sense and it's easier to google how things work. I'm going to mark yours as the answer so far. – SysChaos Dec 5 '19 at 17:39
  • Current PC power supplies have -12V outputs, as there's still a fair number of motherboards being manufactured with serial ports, if only as headers. – Ross Ridge Dec 5 '19 at 19:49

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