Serial Interface COM2 of the Terminal Bases (PM57x, PM58x and PM59x)

Note

Processor Modules with type designator -2ETH (e. g. PM591-2ETH) do not have a COM2 interface.

The serial interface COM2 is connected via a  9-pole SUB-D plug. It is not intended to use COM2 to establish a CS31 system bus. It is configurable for RS-232 or RS-485 and can be used for

  • online access
  • a free protocol
  • Modbus RTU, client and server

If the RS-485 bus is used, each interconnected bus line (each bus segment) must be electrically terminated. The following is necessary:

  • 2 resistors of 120 Ohms each at both line ends (to avoid signal reflections)
  • a pull-up resistor at RxD/TxD-P and a pull-down resistor at RxD/TxD-N. These 2 resistors care for a defined high level on the bus, while there is no data exchange.

It is useful, to activate both the pull-up and the pull-down resistors, which only are necessary once on every bus line, at the bus master.

Pin assignment
Serial Interface Pin        
../_images/087d1a046426a5750a33139001f613591 1 FE Functional earth    
2 TxD RS-232 Transmit data Output
3 RxD/TxD-P RS-485 Receive/Transmit Positive
4 RTS RS-232 Request to send Output
5 SGND Signal ground 0 V supply out  
6 +5 V   5 V supply out  
7 RxD RS-232 Receive data Input
8 RxD/TxD-N RS-485 Receive/Transmit Negative
9 CTS RS-232 Clear to send Input
Shield FE Functional earth    

Attention

:strong:Risk of corrosion!

Unused connectors and slots may corrode, if using XC devices in salt mist environments.

Protect unused connectors and slots with TA535 protective caps for XC devices TA535: Protective Caps TA535 for XC Devices Protective Caps TA535 for XC Devices.

The following drawing shows an RS-485 bus with the bus master at the line end.

../_images/d5fc93b6dd7693430a3313907e410095

RS-485 bus, master at a line end

If the master is located within the bus line, it does not need a terminating resistor. The pull-up and the pull-down resistors, however, are necessary:

../_images/0e7d449cdd77f8e70a33139015cfc7e3

RS-485 bus, master within the bus line

Attention

If the bus is operated with several masters, the pull-up and pull-down resistors may only be installed at one master.

The cable shields must be earthed. See CS31 System Bus CS31 System Bus.