Serial Interface COM2

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

The serial interface COM2 is connected via a 5-pole terminal block and can be used for

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

Note

The serial RS-485 Interface is not electrically isolated.

Note

It is not intended to use COM2 to establish a CS31 system bus.

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.

Note

The pull-up and the pull-down resistors are included inside the Processor Module’s serial RS-485 adaptor. The termination resistor is not included inside the Processor Module and must be connected externally.

It is useful to activate both the pull-up and the pull-down resistors, which are only necessary once on every bus line, at the bus master. For this reason, these 2 resistors are already integrated within the COM2 interface of the Processor Module. They can be activated by connecting the terminals 1-2 and 3-4 of COM2.

Note

For equipping AC500-eCo Processor Modules with a real-time clock and a second serial RS-485 interface COM2, use TA562-RS-RTC serial RS-485 and real-time clock adaptor TA562-RS-RTC - Adapter with Serial RS-485 (COM2) and Real-time Clock.

Pin assignment:

Serial Interface	1	Terminator P
	2	TxD/RxD-P
	3	TxD/RxD-N
	4	Terminator N
	5	Functional earth

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