Modbus programming
Modbus slave communication function
Introduction This page describes the services managed by the slave modules for a Modbus link.
Data exchanges The slave module manages the following requests:
Modbus request
Read n output bits
Read n input bits
Read n output words
Read n input bits
Write an output bit
Write an output word
Write n output bits
Write n output words
Function code / subfunction code
16#01
16#02
16#03
16#04
16#05
16#06
16#0F
16#10
PLC object
%M
%M
%MW
%MW
%M
%MW
%M
%MW
Diagnostics and maintenance
The diagnostics and maintenance information which are accessible from a Modbus link are shown below:
Designation
Read exception status
Echo
Initialize module
Read the diagnostic registers of the PLC
Change end of frame delimiter (ASCII mode)
Switch to listening mode
Reset counters
Number of messages received without CRC error
Number of frames received with CRC error
Number of exceptional responses
Number of messages addressed to the PLC
Number of broadcast messages received
Number of correct responses
Number of messages received in listening mode
Number of invalid characters received
Function code / subfunction code
16#07
16#08 / 16#00
16#08 / 16#01
16#08 / 16#02
16#08 / 16#03
16#08 / 16#04
16#08 / 16#0A
16#08 / 16#0B
16#08 / 16#0C
16#08 / 16#0D
16#08 / 16#0E
16#08 / 16#0F
16#08 / 16#10
16#08 / 16#11
16#08 / 16#12
40
TLX DS COM PL7 xxE
Designation
Read event counter
Read connection event
Read identification
Modbus programming
Function code / subfunction code
16#0B
16#0C
16#11
TLX DS COM PL7 xxE
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