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	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 Ohms 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.

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:

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 System Bus.