ABB AC500 PLC Hardware Manual page 1220

System Assembly, Construction and Connection
AC500-eCo > Connection and Wiring
Fig. 211: Wiring of a straight-through cable
2.5.4.6 Modbus RTU Connection Details
The Modbus RTU protocol is implemented in the AC500 Processor Modules.
Modbus is a master-slave (client-server) protocol. The client sends a request to the server(s)
and receives the response(s).
Available serial interfaces can work as Modbus interfaces simultaneously.
The Modbus client operating mode of an interface is set with the Function Block
COM_MOD_MAST.
Technical data
The Modbus operating mode and the interface parameters are set in the PLC configuration.
Description of the Modbus protocol:
Supported standard
Number of connection points
Protocol
Operating mode
Address
Data transmission control
Data transmission speed
Encoding
Max. cable length for RS-485
1220
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CAUTION!
Risk of communication faults!
When using inappropriate cables, malfunctions in communication may occur.
Only use network cables of the categories 5 (Cat 5, Cat 5e, Cat 6 or Cat 7) or
higher within PROFINET networks.
3ADR010121, 13, en_US
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PM55x and PM56x: EIA RS-485
PM57x, PM58x and PM59x: EIA RS-232 /
RS-485
1 client
Max. 1 server with RS-232 interface
Max. 31 servers with RS-485
Modbus
Client/server
Server only
CRC16
Up to 187.500 baud
1 start bit
8 data bits
1 parity bit, (optional) even, odd, mark or
space
1 or 2 stop bits
1.200 m at 19.200 baud
2019/04/17