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Cable Notes

Rewire Cisco Cable for DECserver

The blue, Cisco console cables (72-3383-01) are nice cables to transform into a serial cable for certain DECservers. These Cisco cables are plenty available and have a distinctive colour compared to standard UTP cable, so it's easy to keep them apart from network cabling. This cable modification applies to DECservers with MJ8 or MMJ serial port connectors (e.g., DECserver 90, DECserver 700-16). You'll need an MJ/MMJ shrink tool, an MJ or MMJ plug, a cutter, and maybe a small knife or saw.

The steps to adapt the Cisco cable for a DECserver are quite simple. But first, some cable pinouts.

Cisco Console Cable Pinout
DB9 MJ8
2 RXD 3 TXD (red) Cisco MJ8 plugcable
opening
side
3 TXD 6 RXD (green)
4 DTR 7 DSR (blue)
5 GND 4 GND (orange)
5 GND 5 GND (yellow)
6 DSR 2 DTR (brown)
7 RTS 8 CTS (grey)
8 CTS 1 RTS (black)

DECserver Pinout
MJ8 MMJ
1 RXD GND DECserver MJ8 plugcable
opening
side
1 DTR DECserver MMJ plugcable
opening
side
2 RXD 2 TXD
3 TXD GND 3 TXD GND
4 CTS 4 RXD GND
5 RTS 5 RXD
6 TXD 6 DSR
7 DTR
8 DSR

Now the steps for the cable modification:

  1. Take the Cisco cable and remove the MJ plug. You can either cut the cable just after the plug and remove a piece of the cable sheath to free the wires, or you can peel off the MJ plug with a saw and remove the contact teeth from the wires.
  2. Ensure the wires are the correct length. This depends on which plug you'll shrink on the cable:
    • MJ: 13 mm
    • MMJ: 7 mm
    Also, for MMJ you'll have to decrease the width of the Cisco cable a little bit because the MMJ plug is narrower (6 pins instead of 8). So, in this case you'll have to narrow the tip of the cable to about 6 mm. This means removing about 1 mm of the sheath on both sides of the cable. The narrowed part should be about 5 mm in length.
  3. Cut the following wires:
    • 4 (orange, GND)
    • 5 (yellow, GND)
    • 1 (black, RTS)
    • 8 (grey, CTS)
    If you want to retain RTS/CTS flow control then do not cut the black and grey wires.
  4. Use the table below to wire an MJ plug or MMJ plug. Use the shrink tool to shrink the plug onto the cable.
  5. Verify the cable with your DECserver.
Cisco Cable to DECserver
DB9 (wire) MJ (pin) MMJ (pin)
RXD (red) 6 TXD 2 TXD
TXD (green) 2 RXD 5 RXD
DTR (blue) 8 DSR 6 DSR
GND - -
DSR (brown) 7 DTR 1 DTR
RTS (grey) 4 CTS -
CTS (black) 5 RTS -
) Optional