HOW TO: Make a serial cable to attach a terminal with a DEC MMJ6 connector to a Digi RJ-45 serial port?

Here is the pinout to attach a terminal or other DTE device to a Digi product which has RJ-45 connectors:

DEC                        Digi
MMJ6                     8-wire RJ45
DSR  1 ------------------ 8 DTR
RxD+ 2 ------------------ 4 TxD
RxD- 3 ---|-------------- 6 SG
TxD- 4 ---|
TxD+ 5 ------------------ 5 RxD
DTR  6 ------------------ 1 DSR (DCD if altpin=on)


  • Pins 3 and 4 on MMJ connector are shorted, then connected to pin 6 on the RJ45 side.
  • The RJ-45 connector used on the Digi side is 8-wire. The altpin setting will determine whether RJ-45 pin 1 is DSR or DCD. altpin=off (DSR), altpin=on (DCD)
Last updated: May 20, 2019

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