Quickly understand RS485 communication message (Brief description of Modbus protocol)
As a widely used industrial automation communication protocol, Modbus protocol realizes data exchange between electronic devices through serial communication lines (such as RS-485) or Ethernet. This article will focus on a brief description of Modbus protocol messages based on RS-485 communication.
1. Common function code description
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Function code |
name |
Remark |
|
16-bit access |
Input Memory |
0x04 |
Read Input Register |
The IO system provides this type of data |
|
Internal memory or physical output memory |
0X03 |
Read Holding Registers |
Change this data through the application | |
|
0X06 |
Writing a single register |
| ||
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0X10 |
Writing multiple registers |
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2. Read the format of function code 0X04
Follow the rule: high digit first, low digit last
Read the value of motor 1 input voltage H0x01F7:
|
Address bits |
Function code |
Register Address |
Number of registers |
CRCCheck code | |||
|
High |
Low |
High |
Low |
High |
Low | ||
|
01 |
04 |
01 |
F7 |
00 |
01 |
slightly | |
Return message:
|
Address bits |
Function code |
Number of bytes |
Register Value |
CRCCheck code | ||
|
High |
Low |
High |
Low | |||
|
01 |
04 |
02 |
00 |
E7 |
slightly | |
3. Write the format of single register function code 0X06
Write the value of motor baud rate H0x0231=5: the factory default baud rate is 115200
|
Address bits |
Function code |
Register Address |
Register Value |
CRCCheck code | |||
|
High |
Low |
High |
Low |
High |
Low | ||
|
01 |
06 |
02 |
31 |
00 |
05 |
slightly | |
Return message: original instruction returns
|
Address bits |
Function code |
Register Address |
Register Value |
CRCCheck code | |||
|
High |
Low |
High |
Low |
High |
Low | ||
|
01 |
06 |
02 |
31 |
00 |
05 |
slightly | |
Setting values and corresponding table with baud rate:
|
hexadecimal |
Baud rate |
|
0 |
9.6Kbps |
|
1 |
9.6Kbps |
|
2 |
19.2Kbps |
|
3 |
38.4Kbps |
|
4 |
57.6Kbps |
|
5 |
115.2Kbps |
|
6 |
256Kbps |
|
7 |
500Kbps |
4. Format of writing multiple registers function code 0X10
Write the value of register address H0230=2; H0x0231=1 of motor 1:
|
Address bits |
Function code |
Register Address |
Number of registers |
Number of bytes |
Register Value |
CRCCheck code | ||||
|
High |
Low |
High |
Low |
High |
Low |
High |
Low | |||
|
01 |
10 |
02 |
30 |
00 |
02 |
04 |
00 01 00 02 |
slightly | ||
Return message:
|
Address bits |
Function code |
Register Address |
Number of registers |
CRCCheck code | |||
|
High |
Low |
High |
Low |
High |
Low | ||
|
01 |
06 |
02 |
30 |
00 |
02 |
slightly | |
5. Quick Reference Table of Instructions
|
project |
instruction | |
|
Read parameters (holding registers) |
01 03 XX XX 00 0Z(CRCslightly) | |
|
Read parameters (input registers) |
01 04 XX XX 00 0Z(CRCslightly) | |
|
Write Parameters |
Parameter size: 1 register |
(CRCslightly)or 01 10 XX XX 00 01 02 yy yy(CRCslightly) |
|
Write Parameters |
Parameter size: 2 registers |
01 10 XX XX 00 02 04 yy yy yy yy(CRCslightly) |
|
Relative Movement in Profile Position Mode |
Switch to position control mode (1-PP mode) |
01 10 03 C2 00 01 02 00 01(CRCslightly) Can be omitted if the motor is in position mode |
|
Write target location |
01 10 03 E7 00 02 04 yy yy yy yy (CRCslightly) The forward and reverse rotation of the motor depends on the positive and negative value of the given position | |
|
Write motion speed |
01 10 03 F8 00 02 04 yy yy yy yy (CRCslightly) | |
|
Starter Motor |
01 10 03 80 00 01 00 06 (CRCslightly) | |
|
Motor ready status |
01 10 03 80 00 01 02 00 07 (CRCslightly) | |
|
Send control word 4F (motor enable, shaft holding) |
01 10 03 80 00 01 02 00 4F (CRCslightly) | |
|
Send control word 5F |
01 10 03 80 00 01 02 00 5F (CRCslightly)(4F-5F motor movement) | |
|
Keep moving |
To modify the target position (if necessary), send control words 4F…5F in sequence. | |
|
Absolute motion in profile position mode |
Switch to position control mode (1-PP mode) |
01 10 03 C2 00 01 02 00 01(CRCslightly) Can be omitted if the motor is in position mode |
|
Write target location |
01 10 03 E7 00 02 04 yy yy yy yy (CRCslightly) The forward and reverse rotation of the motor depends on the positive and negative value of the given position | |
|
Write motion speed |
01 10 03 F8 00 02 04 yy yy yy yy (CRCslightly) | |
|
Starter Motor |
01 10 03 80 00 01 02 00 06 (CRCslightly) | |
|
Motor ready status |
01 10 03 80 00 01 02 00 07 (CRCslightly) | |
|
Send control word 0F (motor enable) |
01 10 03 80 00 01 02 00 0F (CRCslightly) | |
|
Send control word 1F |
01 10 03 80 00 01 02 00 1F (CRCslightly) | |
|
Keep moving |
To modify the target position (if necessary), send control words F→1F; | |
|
Running in profile speed mode |
Switch to profile velocity mode (3-PV mode) |
01 10 03 C2 00 01 02 00 03(CRCslightly) Can be omitted if the motor is in profile speed mode |
|
Set the direction of movement |
01 10 03 F3 00 01 02 00 00(CRCslightly) or 01 10 03 F3 00 01 02 00 40(CRCslightly) | |
|
Write target speed |
01 10 04 48 00 02 04 yy yy yy yy (CRCslightly) | |
|
Starter Motor |
01 10 03 80 00 01 02 00 06 (CRCslightly) | |
|
Motor ready status |
01 10 03 80 00 01 02 00 07 (CRCslightly) | |
|
Send control word 0F |
01 10 03 80 00 01 02 00 0F (CRCslightly) | |
|
Modify running speed |
Modify the running speed (if necessary), and send 0F after modification | |
|
Running in origin return mode |
Switch to origin return mode (6-HM mode) |
01 10 03 C2 00 01 02 00 06(CRCslightly) This can be omitted if the motor is in origin return mode |
|
Origin return method (method: 17-32) |
01 10 04 16 00 01 02 yy yy (CRCslightly) | |
|
Starter Motor |
01 10 03 80 00 01 02 00 06 (CRCslightly) | |
|
Motor ready status |
01 10 03 80 00 01 02 00 07 (CRCslightly) | |
|
Send control word 0F |
01 10 03 80 00 01 02 00 0F (CRCslightly) | |
|
Send control word 1F |
01 10 03 80 00 01 02 00 1F (CRCslightly) | |
|
Motor motion state switching |
Motor emergency stop |
01 10 03 80 00 01 02 01 02 (CRCslightly) Send control word 02 for emergency stop, and send 06-07 first to run |
|
Motor stopped (offline) |
01 10 03 80 00 01 02 00 07 (CRCslightly) Motor free stop | |
|
Motor pause (enable shaft holding) |
01 10 03 80 00 01 02 01 1F (CRCslightly) Send control word 11F to pause (motor is enabled), send 0F to run | |
|
Save parameter H1010:01(H0026) |
01 10 00 26 00 02 04 65 76 61 73 (CRCslightly) | |
|
Restore parameter H1011:01(H003C) |
01 10 00 3C 00 02 04 64 61 6F 6C (CRCslightly) | |
|
Fault reset |
01 10 03 80 00 01 02 00 80 (CRCslightly) After the fault source is cleared, the control word 80 can release the device fault state. | |
