Bronkhorst Modbus slave interface - Manual (Page 22)

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5.3 Bus diagnostics string
The bus diagnostics string can be found in the service report that can be created using FlowFix. The string is also
available as parameter 202 in the Bronkhorst FlowDDE application.
The format of the string is "mAAAA eBBBB sCCCC cDDDD", where AAAA, BBBB, CCCC and DDDD are hexadecimal
representations of 16-bit counters:
• AAAA = bus messages count (CPT1)
• BBBB = bus communication error count (CPT2)
• CCCC = slave message count (CPT4)
• DDDD = bus character overrun count (CPT8)
The following table may be helpful to find the source of communication problems on Modbus. In general, read out
this string after trying to communicate between master and slave, without switching off the power in the meantime.
mAAAA eBBBB sCCCC cDDDD Diagnostics
=0000 =0000 =0000 =0000 No communication detected by slave, check RS485 network,
especially D0 and D1 signals.
>0000 =0000 =0000 =0000 Slave detected valid Modbus messages for other addresses, make
sure master uses correct slave address
=0000 >0000 =0000 =0000 Slave detected invalid messages on the bus, make sure master uses
correct baud rate and parity settings
>0000 >0000 >0000 =0000 Slave detected both valid and invalid messages, make sure RS485
bus termination and polarization are used correctly and the
maximum number of devices is not exceeded. See chapter 2 for
details.
=0000 >0000 =0000 >0000 Slave has received bytes faster than it could process, make sure
master uses correct baud rate. You may want to try a lower baud
rate.
>0000 =0000 >0000 =0000 No problem detected by slave, make sure application timeout of
master is set to a value larger than 100 ms
Page 22 Modbus interface 9.17.035