ABB AC500 PLC Hardware Manual page 1212

System Assembly, Construction and Connection
AC500-eCo > Connection and Wiring
The cable shields must be earthed. See CS31 system bus
on page 1214.
2.5.4.3 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.
Parameter
Standard of the serial interfaces
Interface connectors
Electrical isolation
Serial interface parameters
Operating modes
Supported protocols
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
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 Ω 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.
1212
NOTICE!
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 serial RS-485 Interface is not electrically isolated.
It is not intended to use COM2 to establish a CS31 system bus.
3ADR010121, 13, en_US
Ä Chapter 2.5.4.4 "CS31 bus"
Value
RS-485
COM1: 9-pin D-sub connector (female)
COM2: 5-pole connector with screw-type con-
nection (optional)
none
Configurable by the software
Programming or data exchange
Modbus or serial data exchange using special
software function blocks
2019/04/17