VorTek U44 Series, Instruction Manual

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Series U44 Instruction Manual
M-000-00090
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6.3.2 Modbus Protocol
This Modbus-I Protocol uses RTU transmission mode. The Verification Code uses CRC-16-IBM (polynomial is
X16+X15+X2+1, shield character is 0xA001) which is gained by the cyclic redundancy algorithm method.
Modbus-I RTU mode uses hexadecimals to transmit data.
1.
Modbus-I Protocol Function Code and Format
The flow meter protocol supports the following two-function codes of the Modbus:
Function Code Performance data
0x03 Read register
0x06 Write single register
2.
Modbus Protocol function code 0x03 usage
The host sends out the read register information frame format:
Slave Address Operation
Function Code
First Address Register Register Number Verify Code
1 byte 1 byte 2 bytes 2 bytes 2 bytes
0x01 ~ 0xF7 0x03 0x0000 ~ 0xFFFF 0x0000 ~ 0x7D CRC (Verify)
The slave returns the data frame format:
Slave Address Read Operation
Function Code
Number of Data
Bytes
Data Bytes Verify Code
1 byte 1 byte 1 byte N*x2 byte 2 bytes
0x01 ~ 0xF7 0x03 2xN* N*x2 (Data) CRC (Verify)
N* = Data register number
3.
Modbus Protocol function code 0x06 usage
The host sends a command to write a single register information frame format (function code 0x06):
Slave Address Operation
Function Code
Register Address Register Data Verify Code
1 byte 1 byte 2 bytes 2 bytes 2 bytes
0x01 ~ 0xF7 0x06 0x0000 ~ 0xFFFF 0x0000 ~ 0xFFFF CRC (Verify)