Hi!

I am currently developing a modbus protocol for the slave device. I have a slight confusion as to whether a start of text and an end of text is required for each message frame. If, yes then is there any MODBUS specification for the same? and if no, then how can i know when a frame is over and when a new one begins?

I would really appreciate your comments and suggestions.

Thanking You,
Kushagra

 

Modbus RTU uses "Pauses" to frame messages. 3.5 times the baud rate to be exact.

Dave

 

Read PI-MBUS-300.PDF. From my memory:
ASCII mode - message starts with ":" (Colon), ends with CR, LF
RTU mode - a quiet period of at least 3.5 characters at the particular Baud
rate indicates end of message.
Meir