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Appendix E
Page 147
SCADA-Modbus® System Guidelines
980 SCADA-Modbus “No Response” Troubleshooting Flow Chart (5 of 5)
Verify the correct register
addresses in Appendix H and
change the address of the
registers being requested
as needed.
Check the Modbus device
address in the Communications
Setup menu of the 980.
Change as needed.
Change the baud rate in
either the 980 or the Modbus
server so that both are set
to the same baud rate.
Configure the Modbus server
and MMI to interpret the values
being returned for Units of
Measure as 16-bit integer values.
If you're not sure how to do this,
contact the server or MMI
manufacturer for assistance.
Make a note of the Modbus
message and then call SIGMA
Tech Support to have the
Modbus Response
Message validated.
Configure the Modbus server and/or
MMI to interpret the channel data
being returned as 32-bit floating point
values.If you're not sure how to do
this, conatct the server or MMI
manufacturer for assistance.
Use either a protocol analyzer or a
communications diagnostic program
running on a PC to intercept and
verify the Modbus response message
from the 980.
Are you SURE
the correct register
addresses are being requested
for the values you
want returned?
Are you
SURE the Modbus
deviceaddress of the
980 is correct?
Does the baud
rate of the 980 match that
of the Modbus Server?
Are the
integer values for
Units of Measure being
returned correctly?
Have you
configured the Modbus
server and/or MMI to interpret
the Units of Measure
as integer values?
Have you
configured the Modbus
server and/or MMI, to interpret
the Channel Data being
returned as floating
point values.
NO
NO
NO
YES
YES
NO
YES
YES
NO NO
YES
YES
YES
YES
Returned values do not match
the values in the 980 display.
e.g., If polling for flow, are you requesting register 40033?