ABB AC500 PLC - 2.6.4.12 Modbus RTU Connection Details

Station 32 Station 61
Bus segment 2:
max. 30 stations
+ 2 repeaters
R
Repeater
RR
Repeater
R
Station 1 Station 31
Bus segment 1:
max. 31 stations
+ 1 repeater
R
max. 200 m max. 200 m
Fig. 243: Principle example for a PROFIBUS-DP system with repeaters (1500 kbit/s baud rate)
2.6.4.12 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.
The Modbus operating mode and the interface parameters are set in the PLC configuration.
Description of the Modbus protocol:
Supported standard PM55x and PM56x: EIA RS-485
PM57x, PM58x and PM59x: EIA RS-232 /
RS-485
Number of connection points 1 client
Max. 1 server with RS-232 interface
Max. 31 servers with RS-485
Protocol Modbus
Operating mode Client/server
Address Server only
Data transmission control CRC16
Data transmission speed Up to 187.500 baud
Encoding 1 start bit
8 data bits
1 parity bit, (optional) even, odd, mark or
space
1 or 2 stop bits
Max. cable length for RS-485 1.200 m at 19.200 baud
If a Processor Module provides more than one serial interface, both interfaces (COM1/COM2)
can be operated simultaneously as Modbus interfaces and can operate as Modbus server as
well as Modbus client.
Technical data
System Assembly, Construction and Connection
AC500 (Standard) > Connection and Wiring
2019/04/17 3ADR010121, 13, en_US 1293