Cat5 Null Modem Cable


Original idea, original post, more details

Serial DB9/RJ45 Adapter

    DB9 pin  signal  RJ45 pin    color
    -------  ------  --------    -----
      1       DCD      8         white
      2       RxD      3         black
      3       TxD      1         blue
      4       DTR      5         green
      5       SG       2,6       orange, yellow
      6       DSR      8         white
      7       RTS      4         red
      8       CTS      7         brown
      9       RI       none

Reversed (null-modem) DB9/RJ45 Adapter

    DB9 pin  signal  RJ45 pin    color
    -------  ------  --------    -----
      1       DCD      5         green
      2       RxD      1         blue 
      3       TxD      3         black
      4       DTR      8         white
      5       SG       2,6       orange, yellow
      6       DSR      5         green
      7       RTS      7         brown
      8       CTS      4         red
      9       RI       none

Reversed (null-modem) DB9/RJ45 Adapter w/Loopback

    DB9 pin  signals         RJ45 pin  colors
    -------  --------------  --------  -----------
      2       RxD            1         blue 
      3       TxD            3         black
      5       SG             2,6       orange, yellow
      9       RI       
      1,4,6   DCD, DTR, DSR                            connected
      7,8     RTS,CTS                                  connected
              DCD, DTR, DSR  5,8       green, white    connected
              RTS,CTS        4,7       red, brown      connected

This is useful for things (like IBM AIX boxen) that insist on proper hardware flow control... so we fake it. We're looping both ends from this adapter to we can use a "standard" DB9/RJ45 on the other end.

see also: http://www.lammertbies.nl/comm/info/RS-232_null_modem.html.

Reversed (null-modem) MMJ(M)/RJ45(F) Adapter

    MMJ pin  MMJ signal  RJ45 pin
    -------  ----------  --------
      1       DTR          8
      2       TxD+         3
      3       TxD-         2 / 6
      4       RxD-         2 / 6
      5       RxD+         1
      6       DSR          5
              RTS          (4)
              CTS          (7)

This is useful for DEC equipment having only a DECconnect/MMJ jack. For MMJ, pin 6 is always the edge with the "key". Colors will run either (blue, black, orange, red, green, white) or (white, green, red, orange, black, blue).

see also: http://www.lammertbies.nl/comm/cable/dec-mmj.html. see also: http://h71000.www7.hp.com/wizard/padapters.html

Reversed (null-modem) RJ11(M)/RJ45(F) Adapter

    RJ11 pin  RJ11 signal  RJ45 pin
    --------  -----------  --------
      1        DTR          8
      2        TxD+         3
      3        TxD-         2 / 6
      4        RxD-         2 / 6
      5        RxD+         1
      6        DSR          5
               RTS          (4)
               CTS          (7)

This is for DEC equipment having an RJ11 jack instead of a DECconnect/MMJ jack, such as HSG80s. Pin 1 of the RJ11 plug is on the left-hand side as it get's plugged in.


date: 05/23/2006