MODBUS Communication Protocol
1.Summary:
This protocol complies with the MODBUS communication protocol, adopts the
subset RTU mode of MODBUS protocol, and RS485 half duplex mode.
2.Serial data format:
Serial port settings: no check, 8 bit data, 1 bit stop bits.
For example: 9600, N, 8,1 Meaning: 9600bps, no check, 8 bits, 1 bit stop.
The baud rate of the serial port supported by this transmitter is:
1200,2400,4800,9600,19200,38400,57600,115200
Polynomial of CRC check: 0xA001
The data in the process of data communication is all processed according to
double byte shaping data. If the data is identified as floating point number, the write
needs to read decimal point to determine the size of the data.
3.Communication format:
1. Read command format (03 function code) example:
A.Send read command format:
AD Function Data start Data start Data Nos. Data Nos. CRC16 CRC16
code (H) (L) (H) (L) (L) (H)
0X01 0X03 0X00 0X00 0X00 0X01 0X84 0X0A
B.Return read format:
AD Function Data length Data (H) Data (L) CRC16 CRC16
code (L) (H)
0X01 0X03 0X02 0X00 0X01 0X79 0X84
2.Write command format(06 function code) example:
AD Function Data start Data Data (H) Data (L) CRC16 CRC16
code (H) start (L) (L) (H)
0X01 0X06 0X00 0X00 0X00 0X02 0X08 0X0B
B.Return read format:
AD Function Data Data start Data (H) Data (L) CRC16 CRC16
code start (H) (L) (L) (H)
0X01 0X06 0X00 0X00 0X00 0X02 0X08 0X0B
3.Abnormal response return
AD Function Abnormal code CRC16 CRC16
code (L) (H)
0X01 0X80+ 0x01( Illegal function )
Function 0x02( Illegal Data AD )
code 0x03( Illegal Data )
1
4. Supported commands and commands and data meanings
MODBUS-RTU protocol command list is as follows:
Function Data Data Data
Data range Commands meaning
code start AD Nos. bytes
0x03 Function code reads data
0x03 0x0000 1 2 1-255 Read slave AD
0x03 0x0001 1 2 0-1200 Read baud rate
1-2400
2-4800
3-9600
4-19200
5-38400
6-57600
7-115200
0x03 0x0003 1 2 0-#### Decimal point represents
1-###.# 0-3 decimal places
2-##.## respectively.
3-#.###
0x03 0x0002 1 2 0- Mpa Pressure units
1- Kpa
2- Pa
3- Bar
4- Mbar
5- kg/cm2
6- psi
7- mh2o
8- mmh2o
0x03 0x0004 1 2 -32768-32767 Measured output value
0x03 0x0005 1 2 -32768-32767 Transmitter zero point
0x03 0x0006 1 2 -32768-32767 Transmitter extreme point
0x03 0x000c 1 2 -32768-32767 Zero offset value,
generally is 0
0x06 Function code write data
0x06 0x0000 2 1-255 Rewrite slave AD
0x06 0x0001 2 0-1200 Revise baud rate
1-2400
2-4800
3-9600
4-19200
5-38400
6-57600
7-115200
0x06 0x000c 2 -32768-32767 Zero offset value, pressure
output value = calibration
measurement + zero offset
value.
2
Save and restore factory settings
0x06 0x000F 2 0- Save to
user area
1- Save to
factory area
0X06 0x0010 2 1- Back to
factory
parameters
NOTES:
1. When modifying the baud rate, the transmitter will reply to the modified data at the
baud rate sent by the host. After the reply, the baud rate of the transmitter will become
the modified target value.
2. When modifying the address, the data will be returned with the address before the
modification, and the transmitter address will be automatically modified after the
reply.
3. saving and restoring the factory command will return the original value, indicating
that the transmitter has accepted the command of the host.
4. When restoring factory data, it should be noted that the parameters saved by the
factory may not be the same as those saved by the user, so the address, baud rate and
calibration data may not be the same, so the transmitter must be searched again after
restoring factory parameters.
5. there are only 3 data that users can modify. They are addresses, addresses, baud
rates, and zero offset values.
6. General users are not allowed to modify the calibration data of the transmitter. If
need calibration and change, please contact our company for the transmitter
calibration software. For correction of calibration data, please use our calibration
software.
7. If you need to read the data floating-point identification, such as 6.000. But this
protocol provides that the data are in shaping data communication, so read the data is
6000, and then according to the decimal point position to do the operation, to get
6.000, such as the decimal point is 3, that is 6000/10 (3), is 6000 divided by 10 cubic.
Get 6 of this data.
