The each byte in RTU mode has following format:
8-bit binary, hexadecimal 0-9, A-F
2 hexadecimal characters contained in each 8-bit eld of
the message
4 bytes (32 bits) per parameter.
Floating point format ( to IEEE 754)
Most signicant byte rst (Alternative least signicant byte rst)
Format of Data Bytes
2 byte Cyclical Redundancy Check (CRC)
Error Checking Bytes
1 start bit,
8 data bits, least signicant bit sent rst
1 bit for even/odd parity
1 stop bit if parity is used; 1 or 2 bits if no parity
Byte format
Communication Baud Rate is user selectable from the front panel between 2400, 4800,
9600, 19200 bps.
Exception Cases : An exception code will be generated when the receives instrument
ModBus query with valid parity & error check but which contains some other error
( e.g. Attempt to set oating point variable to an invalid value ) The response generated
will be “Function code” Ored with HEX (80H ). The exception codes are listed below
Function code :
03
Read Holding Registers
Read content of read /write location ( 4X )
04
Read input Registers
Read content of read only location ( 3X )
16
Presets Multiple Registers
Set the content of read / write locations ( 4X )
42
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