After sending any query through software (of the Master), it must allow 300ms of time to elapse before assuming
that the Meter is not going to respond. If slave does not respond within 300 ms, Master can ignore the previous
query and can issue fresh query to the slave.
16 Presets Multiple Registers Set the content of read / write locations ( 4X )
04 Read input Registers Read content of read only location ( 3X )
Read Holding Registers Read content of read /write location ( 4X )
03
Communication Baud Rate is user selectable from the front panel between 4800,9600,19200,38400,57600 bps.
Function code :
8-bit binary, hexadecimal 0-9, A-F
2 hexadecimal characters contained in each 8-bit field of the message
4 bytes (32 bits) per parameter.
Floating point format ( to IEEE 754)
Most significant byte first (Alternative least significant byte first)
Format of Data Bytes
2 byte Cyclical Redundancy Check (CRC)
Error Checking Bytes
1 start bit,
8 data bits, least significant bit sent first
1 bit for even/odd parity
1 stop bit if parity is used; 1 or 2 bits if no parity
Byte format
Each byte in RTU mode has following format:
01 Illegal function The function code is not supported by Meter
02 Illegal Data Address Attempt to access an invalid address or an
attempt to read or write part of a floating point value
03 Illegal DataValue Attempt to set a floating point variable to an invalid value
Exception Cases : An exception code will be generated when Meter receives ModBus query with valid parity
& error check but which contains some other error ( e.g. Attempt to set floating point variable to an invalid value)
The response generated will be “Function code” ORed with HEX (80H ). The exception codes are listed below
3.1 Accessing 3X and 4X register for reading measured values:
Two consecutive 16 bit registers represent one parameter. Refer TABLE 1 for the addresses of 3X and 4X
registers used for parameters measured by the instrument. Each parameter is held in the 3X as well as 4X
registers. Modbus Code 04 and 03 are used to access all parameters in 3X and 4X registers respectively.
Example :
To read parameter,
Voltage2 from 3X: Start address = 00 02 Number of registers = 02
Watt2 from 4X: Start address = 00 0E Number of registers = 02
5
