Difference between Modbus RTU and ASCII

  • Thread starter Manju Ananthanarayanan
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Thread Starter

Manju Ananthanarayanan

I am writing script to test communication of a Modbus slave which supports both Modbus ASCII and RTU. the script runs fine in ASCII, in RTU all my write works but when the data is verified it doesn't match. Is there anything I need to know about even parity in RTU? ASCII I use NULL parity.

Thank you.
The format for each byte in RTU mode is:
Coding System: 8-bit binary, hexadecimal 0-9, A-F

Two hexadecimal characters contained in each 8-bit field of the message.

Bits per Byte: 1 start bit 8 data bits, least significant bit sent first 1 bit for even/odd parity; no bit for no parity; 1 stop bit if parity is used; 2 bits if no parity.

Error Check Field: Cyclical Redundancy Check (CRC).