Operating Mode Modbus Rtu - Eaton M-Max Series Operating Instructions Manual

04/10 MN04020001Z-EN
For Modbus to function at least the following parameters must be
set:
PNU Value
S2.2 1
S2.3 1 - 255
S2.4 0 - 8
S2.6 0/1
6.1 3
6.2 2
Another requirement is that the arrow
of the LCD display is pointing to BUS (adjustable via the LOC/REM
button). The PLC (master) must also be provided with an RS485
serial interface and the necessary Modbus RTU driver software.

Operating mode Modbus RTU

Operating mode Modbus RTU (Remote Terminal Unit) transfers
the data in binary format (faster data rate) and determines the
transfer format for the data request and the data response. Each
message byte that is sent contains two hexadecimal characters
(0 ... 9, A ... F).
Figure 107: Data exchange between master and slave
a Master request
b Slave response, not with broadcast
h The frequency inverter (slave) only sends a response if it
has received a request from the master beforehand.
Notes
To activate Modbus.
Set differently at each slave (MMX); 0 is used by the master for broadcasts.
Same setting at the master and slave.
Same setting at the master and slave.
Fieldbus selected as a control level.
Set setpoint value via the fieldbus; other setpoint sources also possible, fixed frequencies overlay all setpoint values,
also a fieldbus setpoint value.
in the lower status line
C
Address (1 Byte)
Function code (1 Byte)
Data (N x 1 Byte)
Master
Address (1 Byte)
Function code (1 Byte)
Data (N x 1 Byte)
The data transfer between a master (PLC) and the frequency
TM
inverter (M-Max ) is carried out according to the following
sequence:
• Master request: the master sends a Modbus frame to the
frequency inverter.
• Slave response: the frequency inverter sends a Modbus frame as
a response to the master.
a
Start
CRC (2 Bytes)
End
Start
CRC (2 Bytes)
End
b
Modbus parameters
MMX... (Slave)
137