MH OUV-400, Operation Manual

19

20

Start of

frame

Address

Field

Function

Code

Data
Field

Error

Check

End of

Frame

Start Bit

Data Bit

Pari ty

Stop

Frame

1

8

None

2

1

8

Odd

1

1

8

Even

1

1

8

None

1

6. Communication

6.1 Protocol

Using MODBUS communication protocol, 
30 devices/loop (Repeater is need for > 30 devices)

6.2 Transmission

RTU mode, Half-Duplex

6.3 Message Format

6.3.1 Basic Format

Start of Frame : Interval of no transmission equal to or in excess of the 
                          time corresponding to 4 characters
Address Field : Address of all terminals (Range: 1~255)
Function Code : 03H;Read, 06H;Write
Data Field : This field contains information that the slave will use to carry 
                    out the command from the master unit
Error Check : 16 bits CRC
End of Frame : Internal of no transmission equal to or in excess of the 
                         time corresponding to 4 characters

6.3.2 Bit Per Byte: Able to set in the RS485 setting menu 

n, 8, 2
o, 8, 1
E, 8, 1

n, 8, 1

6.4 Read Data Register 

Query:

Start of

Frame

Address

Field

Function

Code

Start

Address

Hi

Start

Address

Lo

Number 

of

Word

Lo

Number 

of

Word

Hi

Error

Check

End of
Frame

01H~FFH

03H

0~nnH

1~nnH

CRC Lo CRC Hi

0~nnH

0H

1 Byte

2 Bytes

1 Byte

2 Bytes

2 Bytes

Response: 

(no error received)

Start of

Frame

Address

Field

Function

Code

Error

Check

End of
Frame

Number of 

Data Bytes

count

D0, D1....Dn

(Hi, Lo, Hi, Lo...)

01H~FFH

03H

CRC Lo CRC Hi

1 Byte

1 Byte

1 Byte

2 Bytes

6.5 Write Data register

Query

Response: 

Single message

Start of

Frame

Address

Field

Function

Code

Start

Address

Lo

Error

Check

End of
Frame

Start

Address

Hi

Value

Hi..

Value
..Lo

01H~FFH

06H

0~nnH

Setting Value

CRC Lo

1 Byte

2 Bytes

2 or 4 Byte

1 Byte

2 Bytes

0~nnH

CRC Hi

01H~FFH

06H

0~nnH

Setting Value

CRC Lo

1 Byte

2 Bytes

2 or 4 Bytes

1 Byte

2 Bytes

0~nnH

CRC Hi

Start of

Frame

Address

Field

Function

Code

Start

Address

Lo

Error

Check

End of
Frame

Start

Address

Hi

Value

Hi..

Value
..Lo

6.6 Error Response 

(Error message received)

Start of

Frame

Address

Field

Function

Code

Error

Check

End of
Frame

Error

Code

01H~FFH

1 Byte

1 Byte

1 Byte

2 Bytes

CRC Lo CRC Hi

83H or 86H

Function Code: The function code requested with MSB set to 1
Error Code: 01: Error Function
                    02: Error Data Address
                    03: Error Data Value