Modbus read-write analog register detailed

Read-Write Analog registers:

Send command (host to slave) format:

[Device Address] [Command Number[High Start register address8bit] [Low8bit] [high number of registers read8bit] [Low8bit] [CRCthe low checksum8bit] [CRCthe High calibration8bit] 

Example:[11][03][00][6B][00][03][CRC low ][CRC high ]

The meanings are as follows:

One: device Address, the address in the example is a, the default address of the dissolved oxygen sensor side is 1,.

A: the command number of the reading analog is fixed to the agreement, which is stipulated in the Modbus protocol.

00 6b : start address high 8 bit (00 , lo 8 bit ( 6b ) : Represents the starting address of the analog that you want to read, such as the starting address in the example is 107 this 006b represents a full address, note that the address here is high 8 bit in front, low 8 bit behind.

00 03 : high register Count 8 bit (00 , lo 8 bit ( 03 ) : Indicates how many simulations are being read from the start address (each of the returned simulations is represented in two bytes). In the example, 3 and the address here is also high 8 bit in front, low 8 bit in the rear .

[CRC low ][CRC high ]: CRC-16 Check at the end of the frame , one of the most important things to note is that the result of the calibration is 8 Lower Bit in front, high 8 bits behind, this order differs from the start address and the address order of the read depth.

Device response: [ device address ] [ command number 03] [ Number of bytes returned ][ data 1][ data 2] ... [ data N][CRC checksum low 8 bit ] [CRC high 8 bit ] 

Example:[11][03][06][02][2B][00][00][00][64][CRC low ][CRC high ]

The meanings are as follows:

One: device address (slave address).

: Command number.

: number of bytes returned (no high two-byte checksum): The number of bytes representing the data, that is, the value of n in data 1,2...n . The example returns 3 analog data because an analog requires 2 bytes, so a total of 6 bytes.

Data1...N: Where[Data1] [Data2]respectively is the first1a high number of analog8bit and low8bit,[Data3] [Data4]is the first2a high number of analog8bit and low8bits, and so on. The values returned in the example are555,0, -.

[CRC Low ][CRC high ]: CRC Check Ibid.

Write a single analog register:

Send command (host to slave) format:

[Device Address] [Command Number[High register address to be placed8bit] [Low8bit] [high data in the lower position8bit] [Low8bit] [CRCthe low checksum8bit] [CRCthe High calibration8bit] 

Example:[11][06][00][01][00][03][CRC low ][CRC high ]

The meanings are as follows:

One: The device address is the same as above.

: The command number to write analog is fixed to .

XX: The register address to be written is 8 bits High and 8 bits lower.

XX: The data to be written is 8 bits High, 8 bits lower. For example, the value of the 1 Register is set to 3.

Note that this command can only write a state of one analog amount.

[ Low 8 -bit CRC check ] [ high 8 -bit CRC check ] Ibid.

Device response: If the command sent by the computer is successfully returned, it will not respond.