Siemens LMV3 series, Technical Instructions, Page: 161 / 224

LMV Series Technical Instructions
Document No. LV3-1000
SCC Inc. Page 1 Section 7
Section 7: Modbus
General
The physical connection to the Modbus system is made via an external OCI412.10 module.
Master-slave principle
Communication between Modbus users takes place according to the master-slave principle. The LMV3
always works as a slave. Every device on the bus line must be assigned a different address.
Data transmission
Modbus interface settings
In addition to the interface parameters that can be set on the LMV3 (parameters 141-149), the following
parameters for the communication interface are already set:
Number of data bits 8
Number of start bits 1
Number of stop bits 1
Transmission mode (RTU)
– The transmission mode used is RTU (Remote Terminal Unit)
– Data is transmitted in a binary format (hexadecimal) with 8 bits
– The LSB (least significant bit) is transmitted first
– ASCII operating mode is not supported
Structure of data blocks
All data blocks use the same structure with the following four fields:
Slave Address Function Code Data Field Checksum CRC16
1 byte 1 byte x byte 2 bytes
Slave Address
Device address of a certain slave
Function Code Function selection (reading / writing words)
Data Field Contains the following information:
- Word address
- Number of words
- Word value
Checksum Identification of transmission errors