Null modem Cable

Μετάβαση στην πλοήγηση Πήδηση στην αναζήτηση


Null Modem Cable is used to connect through a serial connection to the routerboard console using a utility like minicom or hyperterminal. The official name of the cable is "Null modem with loop back handshaking". These cables are not widely available in retail stores so you will most probably have to hack a standard serial cable into a null one by opening up both connectors and rearranging the cable connections to one of them.

Making the cable


  • The best way to do it is by soldering the wires to the connector. So most of the tips apply to this case.
  • All serial connectors have their pins numbered in both sides. This is really useful when you rearrange the wires, because thinking of the connector schematic can be really confusing.
  • Careful with the ground wire! Don't forget to put the insulating cover!
  • Don't heat up to much the connector pins because you may damage the connector.
  • Check the connections with an ohmmeter.

Null modem.png

Connector 1Connector 2Function
1 + 4 + 61+4+6DTRCD + DSR
55Signal ground
7 + 87+8RTSCTS

Connecting to RB

Ok, so now you have a null cable. What now?

-Connect the cable to both the rb and the serial port of your pc.

-Set-up a connection in your hyperterminal/minicom. You need to specify: (at least for rb532 - others may need different options)

  • Serial port (COM1 - /dev/ttyS1)
  • Baud Rate (115200 bits per second)
  • 8 data bits
  • no parity
  • 1 stop bit
  • no hardware folow control

Then you initiate the call and power-on the routerboard. If you are lucky you will immediately see some text spitted out by the rb. If not try changing some of the settings (usually serial port).