ROOTECH ACCURA 7500, User Manual, Page: 21 / 76

Page 21
Packet Communication
Accura 7500 has the following Modbus functions.
Function 03: Read Holding Registers
To read the relay ’s parameter values, the master sends the slave device a Read Holding Registers
request packet. The Read Holding Registers request packet specifies the starting address of the
Holding Register and the word count of the registers to read.
Starting Address is a relative address in Modbus holding register 40000 [40001=0, 40002=1,
40101= 100, etc.]. Refer to Appendix B for CRC generation.
The relay responds to a packet including the value of the register requested.
Request
Slave Function Starting address Word count Error check
03
1 byte 1 byte 2 bytes 2 bytes 2 bytes
Example]
The relay 1 sends data on A phase voltage [ address 40101 ] and B phase voltage [ address 40102 ]
in the following code
via the
Function 03 command.
Slave address = 1, starting address = 64, word count = 2, crc high = 85, crc low = D4
Slave Function Starting Address Word Count Error Check
01 03 00 64 00 02 85 D4
Response
Slave Function Byte Count Data Word 1 --- Data Word N Error Check
03 ---
1 byte 1 byte 1 byte 2 bytes --- 2 bytes 2 bytes
Data word indicates the data required in the request packet.
Example]
The Slave device 1 provides data on A phase voltage(1A1B) and B phase voltage(223B).
Slave address = 1, byte count = 4, crc high = D4, crc low = 5F
Slave Function Byte Count Data Word 1 Data Word N Error Check
01 03 04 1A 1B 22 3B D4 5F