Plug in the loopback dongle (what that is is on the web) and then copy any files to COM1: and watch for activity on the oscilloscope.
Maybe the blinky version of the loopback is better for some like this one.
https://www.google.com/#q=rs232+loopback+test+with+leds
Hello everyone,
I have a used computer systems running MS-DOS v2.0. I need to test the COM port (RS-232). I want to know about the ability to transmit data. How to do it ?
Thanks,

Chowhound
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