Emerson MONITORING OpenComms Instrukcja Użytkownika Pobierz pdf (Strona 23)

Modbus Communication and Connectivity

Data Field(s)

The data field varies in length depending on whether the message is a

request or a response to a packet. This field typically contains infor-

mation required by the slave device to perform the command specified

or to pass back data to the master device.

Error Check Field

The Error Check Field consists of a 16-bit (2 byte) Cyclical Redun-

dancy Check (CRC16). It allows the receiving device to detect a packet

that has been corrupted with transmission errors.

5.5 RTU Framing Examples

5.5.1 Read Registers—Function Code 0x03 & 0x04

Query: for reading holding /input registers (requested by a client)

Response: for reading holding/input registers (response by the

server)

5.5.2 Write Single Holding Register—Function Code 0x06

Query: for writing a single holding register (requested by a client)

Response: for writing a holding registers (response by the server)

Server

Address

Function Code

(0x3/0x4)

Index of starting

Number of

registers to

be read

16 bit

CRC

1 byte 1 byte 2 bytes 2 bytes 2 bytes

Server

Address

Function Code

(0x3/0x4)

Byte

Count

Data from

registers

16 bit

CRC

1 byte 1 byte 1 byte 2*m bytes (= Byte Count) 2 bytes

Server

Address

Function Code

(0x06)

Index of

the register

16 bit value

to be written

16 bit

CRC

1 byte 1 byte 2 bytes 2 bytes 2 bytes

Server

Address

Function Code

(0x06)

Index of

the register

16 bit value

been written

16 bit

CRC

1 byte 1 byte 2 bytes 2 bytes 2 bytes

1 2 ... 18 19 20 21 22 23 24 25 26 27 28 ... 47 48

Komentarze do niniejszej Instrukcji

Brak uwag

Emerson MONITORING OpenComms Instrukcja Użytkownika Strona 23

Komentarze do niniejszej Instrukcji

Powiązane produkty i podręczniki dla Networking Emerson MONITORING OpenComms