Configuring the fieldbus
6.2 Communication via RS485
Inverter with CU240B-2 and CU240E-2 Control Units
Operating Instructions, 01/2011, FW 4.4, A5E02299792B AB
139
6.2.3.3 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.
Character delay time
Character delay time
Character delay time
Character delay time
Character delay time
Character delay time
≥ 3.5 bytes
≥ 3.5 bytes
Initial pause Interframe
delay
Function
code
Data
Initial
pause
Interframe
delay
Interframe
delay
End pause
Slave
1 Byte
1 Byte 1 Byte 1 Byte 1 Byte 1 Byte 1 Byte
CRC low CRC high
1 Byte 0 ... 252 Bytes
2 Byte
CRC
3URWRFRO'DWD8QLW3'8
$SSOLNDWLRQ'DWD8QLW0RGEXVIUDPH
0RGEXV5787HOHJUDPP
$SSOLNDWLRQ'DWD8QLW
0RGEXVIUDPH
$SSOLNDWLRQ'DWD8QLW
0RGEXVIUDPH
Figure 6-12 Modbus with delay times
The data area of the telegram is structured according to the mapping tables.
Commentaires sur ces manuels