Instrument Control (GPIB, Serial, VISA, IVI)

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modbus RTU interframe and intermessage delay considerations

Hi All,

 

I understand the Modbus RTU protocol as described on ni website (http://www.ni.com/white-paper/7675/en)
I went inside the Modbus Library and studied all the VIs. I would like to understand that as mentioned in the above link, how are the interframe and intermessage delays handled.

 

Modbus.jpg

 

I see that the interframe delay is >3.5 char and intermessage is 1.5 char. But I didn't see any of these considerations being implemented in the code.

Can anyone please throw some light on this?

 

Thanks.

 

Best Regards,

 

Ujjval Shah

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A lot of communication stuff like protocols are developed years ago. The performance of the Computers (ModBus masters and slaves) in those days made it necessary to give the CPU some time before sending data.

I think that these ModBus delays are specified for that purpose.

 

A lot of ModBus communication I program myself. I never noticed any error in communication with a ModBus slave during testing and I never use these delays.

 

Regards, Kees

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