ECD DO82, Instructional Manual

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HYDRA-DS NO
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C. MODBUS RTU R
EGISTER
L
ISTING
03 (0x03) Read Holding Registers
This function code is used to read the contents of a contiguous block of holding registers in a remote device. The Request
Protocol Data Unit specifies the starting register address and the number of registers. In the Protocol Data unit Registers
are addressed starting at zero. Therefore registers numbered 1-16 are address as 0-15.
The register data in the response message are packed as to byte per register, with the binary contents right justified
within each byte. For each register, the first byte contains the high order bits and the second contains the low order
bits.
Request
Modbus ID (Slave Address)
1 Byte 1 to 247 (0x01 to 0xF7)
Function code 1 Byte 0x03
Starting Address 2 Bytes 0x0000 to 0xFFFF
Quantity of Registers 2 Bytes 1 to 125 (0x01 to 0x7D)
CRC 2 Bytes calculated
Request
Modbus ID (Slave Address) 1 Byte 1 to 247 (0x01 to oxF7)
Function code 1 Byte 0x03
Byte Count 1 Byte 2 x N*
Register Value(s)
*N x2 Bytes
CRC
2 Bytes calculated
*N = Quantity of Registers
Error
Modbus ID (Slave Address)
1 Byte 1 to 247 (0x01 to 0xF7)
Error Code 1 Byte 0x86
Exception Code
1 Byte 01, 02, 03, or 04
CRC 2 Bytes calculated
06 (0x06) Write Single Register
This function code is used to write a single holding register in a remote device. The Request Protocol Data Unit specifies
the address of the register to be written. Registers are addressed starting at zero. Therefore register number 1 is
addressed as 0. The normal response is an echo of the request, returned after the register contents have been written.
Request
Modbus ID (Slave Address)
1 Byte 1 to 247 (0x01 to 0xF7)
Function code 1 Byte 0x06
Register Address
2 Bytes 0x0000 to 0xFFFF
Register Value 2 Bytes 0x0000 to 0xFFFF
CRC 2 Bytes calculated
Response
Modbus ID (Slave Address) 1 Byte 1 to 247 (0x01 to 0xF7)
Function code 1 Byte 0x06
Register Address
2 Bytes 0x0000 to 0xFFFF
Register Value 2 Bytes 0x0000 to 0xFFFF
CRC 2 Bytes calculated
*N = Quantity of Registers