Communication Over Modbus Rtu - Siemens Sinamics G120P Operating Instructions Manual

Operation
6.8 Communication via RS485
6.8.3

Communication over Modbus RTU

Overview of communication using Modbus
The Modbus protocol is a communication protocol with linear topology based on a
master/slave architecture.
Modbus offers three transmission modes:
● Modbus ASCII
Data in ASCII code. The data throughput is lower compared to RTU.
● Modbus RTU (RTU: Remote Terminal Unit)
Data in binary format. The data throughput is greater than in ASCII code.
● Modbus TCP
Data as TCP/IP packets. TCP port 502 is reserved for Modbus TCP. Modbus TCP is
currently undergoing definition as a standard (IEC PAS 62030 (pre-standard)).
The Control Unit supports Modbus RTU as a slave with even parity.
Communication settings
● Communication using Modbus RTU takes place over the RS485 interface with a
maximum of 247 slaves.
● The maximum cable length is 100 m.
● Two 100 kΩ resistors are provided to polarize the receive and send cables.
Note
It is not permitted to change over the units
The "Unit changeover (Page 374)" function is not permissible with this bus system!
230
Inverter cabinet units
Operating Instructions, 12/2014, A5E32923362A