Re-Wiring the Serial Port

The serial ports on the 171 CBU 78090, 171 CBU 98090 and 171 CBU 98091 processors support 2-wire RS485 communication. Some existing Momentum networks may include devices that employ 4-wire RS485 communication. In such cases, you need to convert the existing 4-wire connections to 2-wire connections at the processor.

The solution is:

• join together the Tx+ and Rx+ signals, then connect them to pin 3 (D1) of an RJ45 serial port connector on the processor

• join together the Tx- and Rx- signals, then connect them to pin 6 (D0) of an RJ45 serial port connector on the processor

• connect the single-wire Gnd signal to pin 5 (Gnd) of an RJ45 serial port connector on the processor

These wiring changes are depicted, below:

Every other pin on the processor RJ45 serial port connector is reserved, except for pin number 8, to which a cable shield is connected if you are using shielded wiring.