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Retrocomputing

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    Well, it would help if you could tell about your configuration - not at least about what 'device' that is you want to receive data from. Also, why you can't check the switches you already know about? Commented Aug 24, 2018 at 22:22
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    Assuming you had the correct serial settings, what does the device do with received characters? Does it echo them? Are there any "safe" characters (e.g. space, linefeed) that could be input without modifying the internal state of the device? Commented Aug 25, 2018 at 0:49
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    Do you have access to either an oscilloscope or a logic analyzer? Commented Aug 25, 2018 at 3:10
  • Also, what do you know about the software / protocol on the device? The "white squares" are an encouraging sign that there is at least something using the port. Do you know for certain that it uses a text-based (not binary) protocol? Is it a remote terminal or login session? Commented Aug 25, 2018 at 3:29
  • This is a specific response for your hardware, so wouldn't make a good answer. According to the Liebert RAC2-8-EK manual the device can run at 1200, 2400, 4800 or 9600 baud (schematic, last page). You can only change baud rate with the power off, as the switches are behind the panel. The ports are at RS-232 level ("EIA-232 ports"). The serial port mirrors the front panel access, and so may be a simple ASCII menu. As there's no mention of word size or parity, it's likely 8N1. So you've got four options to try from the start. Commented Aug 26, 2018 at 17:47