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I have a USB-RS232C adaptor. Plugging it into my computer nicely provides a COMx port.

The device I want to connect to specifies that SD and RD should be switched. My assumption is that this refers to the channels more commonly specified as RxD and TxD. The tool used to do this (in the absence of rewiring) is a 'null-modem' adaptor.

Is it possible to emulate the presence of a null-modem adaptor on the computer, to save

  • buying a physical adaptor
  • rewiring the existing cable
  • writing some obscenely convoluted driver?

This question (Faking an RS232 Serial Port) has some answers that look plausible, but they seem to refer to emulating the entire setup - I already have a COM port and just want to switch a pair of signals.

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chrisb2244
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    No, there is no way to emulate what you need. No, a driver cannot substitute for a null-modem adapter. You have to perform the swap somewhere in hardware so that the input is connected to an output (rather than input to input and output to output). – sawdust Mar 08 '16 at 06:16
  • Try to search for Virtual Null Modem. On Windows I have used this application in the past. – Helen Downs Mar 08 '16 at 09:08

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