RS-449 Null Modem Cables

The following diagram illustrates a synchronous null modem cable that allows you to connect two Sun machines that each supply clocking, using the RS-449 interface. Each Sun machine supplies clocking on pins 17 and 35. The null modem cable routes this clocking to pins 8 and 26 on the opposite side to provide receive clocking.

Because the RS-449 interface is balanced, there are two pins for each signal. For example, in the diagram below, Send Data (SD), pins 4 and 22, is connected to Receive Data (RD), pins 6 and 24. This means that pin 4 is connected to pin 6 and pin 22 is connected to pin 24.

In x25tool Link Editor window, set the Tx Clock parameter to the bit rate you want (not External) on both machines.

Figure A-3 RS-449 Null Modem Cable: Both Machines Supply Clocking

The following diagram illustrates a synchronous null modem cable that allows you to connect a Sun machine to another Sun or non-Sun machine, using the RS-449 interface. The Sun machine supplies both the transmit and receive clocks for the other machine. Note that this null modem cable is not symmetrical.

Because the RS-449 interface is balanced, there are two pins for each signal. For example, in the diagram below, Send Data (SD), pins 4 and 22, is connected to Receive Data (RD), pins 6 and 24. This means that pin 4 is connected to pin 6 and pin 22 is connected to pin 24.

In x25tool Link Editor, set the Tx Clock parameter to the bit rate you want (not External) on the Sun machine that is to supply clocking.

Figure A-4 RS-449 Null Modem Cable: Sun Machine Supplies Clocking