User Manual

11.8.2 Instruction Set in MODBUS-RTU Protocol
With the MODBUS-protocol the data are read and written via
register accesses. The following register accesses are defined
for the communication with the sensor modules:
Function number Function
03 hex Read Holding Register (Read/Write-Register)
04 hex Read Input Register (Read-Only-Register)
06 hex Pre-set Single Register
08 hex Diagnostic
10 hex Pre-set Multiple Register
Table 11.15 MODBUS commands
Read Holding Register
Description:
By this command input/output registers (read/write registers)
can be read.
request telegram
ADR FNR REGSTA REGNUM CRC
03 MSB LSB MSB LSB MSB LSB
response telegram
ADR FNR BYTNUM D0 D1
03
…
Dn CRC
MSB LSB
ADR ............ module address (hex 00..7F)
FNR ............ function number (hex 03)
REGSTA ..... address of the first register to be read
REGNUM .... number of registers to be read
Hardware Manual COMBILOG 1022
130