Modbus Rtu Telegram - Siemens SINAMICS G120 Operating Instructions Manual

Parameter
p2029
p2040
8.4.3.3

Modbus RTU telegram

Description
For Modbus, there is precisely one master and up to 247 slaves. Communication is always
triggered by the master. 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.
Initial
pause
Initial pause
Slave
≥ 3.5 bytes 1 Byte
≥ 3.5 bytes 1 Byte
Figure 8-16 Modbus with delay times
The data area of the telegram is structured according to the mapping tables.
SINAMICS G120C frequency converter
Operating Instructions, 03/2012, FW V4.5, A5E02999804B AB
Description
Fieldbus fault statistics
Displays receive faults on the fieldbus interface
Process data monitoring time
Determines the time after which an alarm is generated if no process data are
transferred.
Note: This time must be adapted depending on the number of slaves and the baud rate
set for the bus (factory setting = 100 ms).
interframe
delay
Function
code
1 Byte 0 ... 252 Bytes
1 Byte 1 Byte
interframe
delay
data
CRC low CRC high
1 Byte 1 Byte
Configuring the fieldbus
8.4 Communication via RS485
Interframe
delay
CRC
2 Byte
1 Byte
End
pause
123