3.1.1modbus Format description

Read command (take slave 0x01 as an example)

Slave

addr

Function

number

Register

High addr

Register

Low addr

Data

H

Data

L

CRC Check

L

CRC

Check H

DR

RW

RegH

RegL

DH

DL

CL

CH

0x01

0x03

RegH

RegL

DH

DL

CL

CH

Sensor return

Slave

addr

Function

number

Number of

data bytes

Data byte 1

high bit

Data byte 1

low bit

···

CRC Check

L

CRC

Check H

DR

RW

D

DATA1H

DATA1L

···

CL

CH

0x01

0x03

D

DATA1H

DATA1L

···

CL

CH

Example: Host sends: 01 03 00 10 00 01 85 CF

Read the ranging value of 1 slave

Module

reply:

01 03 02 00 15 79 8B

Ranging value is 0x0015 (21mm)

Write command (take slave 0x01 as an example)

Slave

addr

Function

number

Register

High addr

Register

Low addr

Data

H

Data

L

CRC Check

L

CRC

Check H

DR

RW

RegH

RegL

DH

DL

CL

CH

0x01

0x06

RegH

RegL

DH

DL

CL

CH

Sensor return

Slave

addr

Function

number

Number of

data bytes

Data byte 1

high bit

Data byte 1

low bit

···

CRC Check

L

CRC

Check H

DR

RW

RegH

RegL

DH

DL

CL

CH

0x01

0x06

RegH

RegL

DH

DL

CL

CH

Example: Host sends: 01 06 00 04 00 01 09 CB

Set the ranging mode of 1 slave to

high precision

Module

reply:

01 06 00 04 00 01 09 CB

Set successful response

Special note: CRC check rule is CRC-16/MODBUS X16+X15+X2+1

The check code can be generated by the existing CRC check code generator or the

matching module, which is convenient to use.