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V2 AC500 Hardware 1-43 System data AC500 / Issued: 05.2007
Modbus
General
The Modbus protocol is used all over the world. The MODICON Modbus
®
RTU protocol is integrated in
the AC500 CPUs.
Numerous automation devices, such as PLC installations, displays, variable-frequency inverters or
monitoring systems, for instance, have a Modbus
®
RTU interface by default or as an option and can
therefore communicate with the AC500 CPUs without any problems via the serial interfaces COM1 and
COM2 (RS-232 or RS-485).
Modbus
®
is a master-slave protocol. The master sends a request to the slave and receives its response.
Both interfaces COM1 and COM2 can work as Modbus
®
interfaces simultaneously.
The Modbus
®
operating mode of an interface is set with several function blocks.
Bus topology
Point-to-point with RS-232 or bus topology with RS-485. Modbus
®
is a master-slave protocol..
Technical data
Supported standards EIA RS-232 or EIA RS-485
Number of connection points 1 master
max. 1 slave with RS-232 interface
max. 32 slaves with RS-485 interface
Protocol Modbus
®
(master/slave)
Check sum CRC 16
Data transmission rate up to 19200 baud
Character frame 1 start bit,
8 data bits,
1 parity bit, even or odd (optional)
1 or 2 stop bit(s)
Maximum cable length for RS-485: 1200 m with 19200 Baud
Number of user data, bus cycle time and data security
See relevant chapters in the operating manual
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