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I want to connect a vintage 70s era terminal with a Raspberry Pi. The terminal uses a DB-25 connector and features hardware flow control (RTS/CTS/DTR etc). What would be the recommended way to hook it with RPi to get the most "authentic" experience out of it?

It seems that either the GPIO pins + voltage level converter or a USB-serial cable could be used. But I don't know if one of these approaches is better than the other for driving a hardware terminal.

Additional information: The terminal manual mentions that the port voltage swings from -10V to 10V. Thus the need for a voltage level converter when used with GPIO.

  • Sounds like you're asking for an opinion. You might argue that building your own interface to the 3.3v TTL GPIO is more authentic but will lack the built-in control lines you need. Using a USB adaptor will be easier but might not give you the "true" RS232C input your equipment needs with out some extra work. – Roger Jones Nov 21 '19 at 14:05
  • @RogerJones I don't think there are more options than these two. If there are, I'd be interested. Also advice for what kind of specs should I look if I go the USB cable way would be nice. There seem to be a ton of different options, but haven't found one mentioning RS232C explicitly (only RS232, which leaves unclear if "C" is implied). – m000 Nov 21 '19 at 15:31
  • I meant RS-232 revision C. From wikipedia: "Changes since Revision C have been in timing and details intended to improve harmonization with the CCITT standard V.24, but equipment built to the current standard will interoperate with older versions.". Revision C, I believe, was the last one to only specify the 25-pin connector you have. – Roger Jones Nov 22 '19 at 8:37
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    Thinking some more about it I don't think using the GPIO will work as the UART has no hardware control lines. I'd try something along the lines of a FT232R module to get a full compliment of UART lines on the USB and then several MAX233A chips (and an external 5v supply, maybe) to interface that to your DB25 connector. As @Milliways points out though, the typical ±8V the MAX233A gives you might not be enough for the DTE you have. – Roger Jones Nov 22 '19 at 8:54
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This is not really a Pi question, however you CAN NOT connect a RS232 terminal to GPIO (even with a level converter) because the polarity is reversed.

You MAY be able to use a RS232 converter (or RS232 USB adapter) - BUT most of these output 0V - 5V signals, which is not RS232 compliant (RS232 are bipolar ±15V) but similar to signals generated by older computers (1990 vintage).

Some vintage terminals may work with 0V - 5V, but computers haven't output true RS232 since the 1980s - and even then they were uncommon.

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