Siemens SINAMICS G120 - Modbus RTU Telegram; Baud Rates and Mapping Tables

Configuring the fieldbus
7.6 Communication via RS485
Inverter with CU230P-2 Control Units
164 Operating Instructions, 11/2013, FW V4.6.6, A5E02430659B AG
7.6.3.2
Modbus RTU telegram
Description
For Modbus, there is precisely one master and up to 247 slaves. The master always starts
the communication. The slaves can only transfer data at the request of the master. Slave-to-
slave communication is not possible. The Control Unit always operates as slave.
The following figure shows the structure of a Modbus RTU telegram.
Figure 7-17 Modbus with delay times
The data area of the telegram is structured according to the mapping tables.
7.6.3.3
Baud rates and mapping tables
Permissible baud rates and telegram delay
The Modbus RTU telegram requires pauses for the following cases:
● Start detection
● Between the individual frames
● End detection
Minimum duration: Processing time for 3.5 bytes (can be set via p2024[2]).
A character delay time is also permitted between the individual bytes of a frame. Maximum
duration: Processing time for 1.5 bytes (can be set via p2024[1]).