Modbus RTU Protocol V6

MODBUS Protocol V6.5
MODBUS RTU PROTOCOL

This communication protocol adopts the standard ModBus protocol and the RTU (hexadecimal number) transmission mode. The ModBus protocol is a master-slave protocol.
Here, the host computer is the master station and the rectifier is the slave station.
address: 1-32 Function code: including reading and writing multiple registers. Data: transmitted in binary code. CRC16: Cyclic redundancy check, check from the slave station address to the last byte of the data area, and calculate the polynomial code as A001 (hex).
1. Communication port settings:
Communication method Asynchronous serial communication interface, RS-485. Rate 19200bps
2. Byte data format HEX:
.1 start bit .8 data bits .1 stop bit .Even parity

1

*

*

*

*

*

*

*

*

1 *

Start bit

Data bit (from low to high)

Stop bit check

3. Example of message frame format (read and write functions are

defined from the perspective of the master station):

Read register frame

Slave address

Function code

First register address Number of registers N

1byte

1byte

2byte

2byte

01H

03H

0000H

0002H

CRC16 2byte CrcL, CrcH

Read register return frame

Slave address

Function code

Number of bytes

Register data

CRC16

www.ato.com [email protected] Globle Shipping +1 800-585-1519

MODBUS Protocol V6.5

1byte 01H

1byte 03H

1byte 04H

N*2byte 0000H 0000H

2byte CrcL, CrcH

Write register frame

Slave

Function

address

code

1byte

1byte

01H

10H

First register address 2byte 0005H

Number of registersN
2byte 0002 H

Number of bytes 1byte
04H

Register data
N*2byte 0000H 0000H

CRC16
2byte CrcL, CrcH

Write register return frame

Slave

Function

address

code

1byte

1byte

01H

10H

First register address 2byte 0005H

Number of registersN
2byte 0002H

CRC16
2byte CrcL, CrcH

Function code table

Function code

ModBus name

03H

Read Holding Registers

10H

Write Multiple Registers

Function name
Read N register values
Write N register values

broadc ast No
No

Quantity 3 2

4. Register address table (read and write registers)：

Numbering

Parameter symbol

1

V

2

I

parameter name
Voltage display value
Current display value

address

Types of

0

1

Value range
0-9999 (10Base) 0-9999 (10Base)

0-3

3

ZT

State value

2

Read

(10Base)

and

write

Communication

4

TX

3

0

counter

Remarks
0——normal 1——overheat 2——Overcurrent 3——Other failures The host computer accumulates the value regularly, and the communication interruption is displayed after the value is greater than

www.ato.com [email protected] Globle Shipping +1 800-585-1519

5

F

Desired point

4

6

SW

Number of switches

5

MODBUS Protocol V6.5

0-9999 (10Base)

the set value

0000H-0103H (16Base)

Specific reference to control bit variables

Control bit variable

Digits

8

1

start up

0

stop

7 6 54

3

2

alarm

No alert

1 Reverse Positive

0 Stabilization Steady flow

Register address table description: 1. All data types are unsigned integer (two bytes). 2. All data with decimal points in communication transmission are replaced by integers. For example, 1.000 is replaced by 1000.(That is, the decimal point is ignored) 27.9 is replaced by 279.
3. All register data is represented by hexadecimal numbers during the transmission process. The high byte is transmitted first, and then the low byte. For example, when transmitting 279, first transmit 01H and then 23H.

www.ato.com [email protected] Globle Shipping +1 800-585-1519