Theodor Friedrichs COMBILOG 1020, Hardware Manual

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Hardware Manual COMBILOG 1020
132
11.8.3
Instruction Set in MODBUS-RTU-Protocol
With the MODBUS-protocol the data are read and written via reg-
ister accesses. The following register accesses are defined for
the com-munication 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 Dn CRC
03
…
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
BYTNUM ..... number of databytes (max. 64)