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How do I make an RS232 Loop Back Plug?

Solution:

Pinouts for making a RS232 Loop Back connector. The DB-25 Loop Back connector plug consists of a female DB-25 connector wired as follows:

  • Pin 4 connected to pins 22 and 5 (RTS to RI and CTS)
  • Pin 2 connected to pin 3 (TxD to RxD)
  • Pin 20 connected to pins 6 and 8 (DTR to DSR and DCD) 

  • The RJ-45 Loop Back connector consists of a single 10 pin RJ-45 (shipped with Digi products) plug wired as follows:

  • Pin 3 connected to pins 1 and 8 (RTS to RI and CTS)
  • Pin 5 connected to pins 6 (TxD to RxD)
  • Pin 9 connected to pins 2 and 10 (DTR to DSR and DCD)

  • The RJ-45 Loop Back connector consists of a single 8 pin RJ-45 plug wired as follows:

    The DB-9 Loop Back connector consists of a female DB-9 connector wired as follows:

  • Pin 8 connected to pins 7 and 9 (CTS to RTS and RI)
  • Pin 3 connected to pin 2  (TxD to RxD)
  • Pin 4 connected to pins 6 and 1 (DTR to DSR and DCD)
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