Scada-Modbus "No-Response" Troubleshooting Flow Chart (4 Of 5) - Sigma 980 Operating And Maintenance Manual

Appendix E

980 SCADA-Modbus "No-Response" Troubleshooting Flow Chart (4 of 5)

Continued from sheet 3.
Is the
980 responding now?
NO
Put the RX and TX
wires back to the way
they were before.
Does the
Modbus message start
with a colon and end with
a carriage return and
Line Feed pair?
YES YES
Does the
message address
match the Modbus device
address of the
980?
The first two characters in the message, after the colon, denote
the Modbus device address in Hexadecimal.
YES YES
Make a note of the Modbus
message and then call our
tech support to have the
Modbus message validated.
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SCADA-Modbus® System Guidelines
Congratulations!
YES
You have fixed it.
Use either a protocol analyzer
or a communications program
such as Windows Terminal or
Comit running on a PC in place
of the 980 to intercept and verify
the Modbus polling request
being sent from the Master
device to the 980.
NO
NO
Is the Modbus
NO
message
being received?
YES YES
The problem is in either the
Modbus Master (polling) device
or the communications media.
Correct problem and then
check for a response again.
Either change the Modbus
device address of the 980 or
change the address in the
Modbus server.