Serial Interface COM1

The serial interfaces COM1 and COM2 are designed according to the standard EIA RS-485. Both interfaces can be operated in RS-485 mode.

Standard of the serial interfaces RS-485
Interface connectors

COM1: 9-pole Sub-D connector (female)

COM2: 5-pole connector with screw-type connection (optional)
Electrical isolation none
Serial interface parameters Configurable by the software
Operating modes Programming or data exchange
Supported protocols MODBUS or serial data exchange using special software function blocks
Pin assignment
Serial Interface Pin Signal Description

Serial Interface

../_images/087d1a046426a5750a33139001f61359 		1 FE Functional earth
2 SGND 0 V power supply, internally connected to M terminal
3 RxD/TxD-P Receive/Transmit positive
4 Reserved Reserved, not connected
5 SGND 0 V power supply, internally connected to M terminal
6 +3.3 V 3.3 V power supply
7 Reserved Reserved, not connected
8 RxD/TxD-N Receive/Transmit negative
9 Reserved Reserved, not connected
Shield Cable shield Functional earth

The serial non-isolated interface COM1 is connected to a 9-pole SUB-D connector. It is configurable for RS-485 and can be used for:

  • online access with Automation_Builder (via RS-485 programming cable e. g. TK504 TK504 - Programming Cable),
  • as MODBUS RTU, client and server
  • for ASCII serial protocols
  • a CS31 system bus (RS-485), as master only.

Note

The serial RS-485 interface is not electrically isolated.

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 Ohm each at both line ends (to avoid signal reflections)
  • In addition, 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.

Note

The pull-up, pull-down and termination resistors are not included inside the Processor Module and must be connected externally.

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

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

../_images/68c0e8f2e389179c0a33139000eba54e

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/0e411738e38917da0a33139000eba54e

Attention

:strong:Risk of EMC disturbances!

Unshielded cables may cause EMC disturbances.

Always use shielded cables and connect the shield at every device.

Attention

:strong:Risk of malfunctions!

The pull-up resistors must be used only one time within a bus line.

Use the pull-up resistors only at 1 master.

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