Modbus TCPIP Slave program problem

A

Thread Starter

amar

Hello,

I have written program using VB6, which implements modbus protocol and talk to server using fc-code(04). and its working very good for first request. But after that not able to receive response from server.

Please help
 
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Lynn August Linse

Do make sure you change the header sequence number between polls. In theory you don't need to, but some slave MIGHT discard a second request with same number as a duplicate.

I would not expect this to be common in MB/TCP, but someone who (for example comes from the AB/Rockwell world) will assume this is the correct behavior.
 
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