Search FAQs

You are currently viewing the content available in Vietnam. If you are looking for information for another region, please select the correct country from the top-left dropdown in the page and 'Navigate to Browse FAQs' in the Support menu.

When using a Unity Premium PLC, what function block would I use for retrieving diagnostic information from a Modbus slave device?

Issue:
Function block to use in a Premium PLC for retrieving diagnostic information from a Modbus slave device

Product Line:
Premium PLC, Unity Pro

Resolution:
The SEND_REQ function block is used for retrieving diagnostic and maintenance information from a Modbus slave device....

Modbus Request	Function Code / Sub Function Code	Communication Function
Exception status	16#07	SEND_REQ
Diagnostics	16#08/16#xx	SEND_REQ
Event counter	16#0B	SEND_REQ
Connection event	16#0C	SEND_REQ
Slave identification	16#11	SEND_REQ

The diagnostics and maintenance information are shown below:

Designation	Function code / sub-function code
Read exception status	16#07
Echo	16#08 / 16#00
Initialize module	16#08 / 16#01
Read the diagnostic registers of the PLC	16#08 / 16#02
Change end of frame delimiter (ASCII mode)	16#08 / 16#03
Switch to listening mode	16#08 / 16#04
Reset counters	16#08 / 16#0A
Number of messages received without CRC error	16#08 / 16#0B
Number of frames received with CRC error	16#08 / 16#0C
Number of exceptional responses	16#08 / 16#0D
Number of messages addressed to the PLC	16#08 / 16#0E
Number of broadcast messages received	16#08 / 16#0F
Number of correct responses	16#08 / 16#10
Number of messages received in listening mode	16#08 / 16#11
Number of invalid characters received	16#08 / 16#12
Read event counter	16#0B
Read connection event	16#0C
Read identification	16#11