plc and scada interfacing problem

Join Date
Mar 2015
Location
mumbai
Posts
2
I'm trying to interface plc and scada where scada is monitoring and controlling the parameter using MODBUSA3 protocol but SCADA is not sending 05 function code to write the coil(on/off he coil).I'm using Vijeo Citect Scada 7.2.please help me.
 
1). Are you writing the correct value?

Statement below is from the Modbus standard:

A value of FF 00 hex requests the output to be ON. A value of 00 00 requests it to be OFF. All other values are illegal and will not affect the output.

2). Does the Modbus connection work otherwise? Does the Scada read data from the PLC?
 
If the master executes a read, but will not execute a write, then

1) the slave register the master is addressing is not writeable, it is read only
2) The slave register the master is addressing does not exist or is undefined
3) The master is writing an unacceptable value
4) The master does not implement the 05 function code (unlikely)
 

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