Beckhoff BC7300 Manuel d'utilisateur télécharger pdf (Page 28)

MODBUS

28 BC7300

Byte Name

Example RTU ASCII

Start frame

„:“ 0x3A

Slave address

11 0x0B „0B“ 0x30, 0x42

Function code

1 0x01 „01“ 0x30, 0x31

Byte Count

2 0x02 „02“ 0x30, 0x32

Data bits 0..7

4 0x04 „04“ 0x30, 0x34

Data bits 8..15

0 0x00 „00“ 0x30, 0x30

Error Check

LRC / CRC

0x23

0x3D

„EE“ 0x45, 0x45

End of frame

t1-t2-t3 CRLF 0xD, 0xA

Read Digital Inputs (Function 2)

READ INPUT STATUS

Function 2 can be used to read the digital input data.

In this example the first 10 digital inputs of slave number 11 are read. The

start address is zero. If an offset is to be entered, this is done in the "Start

address" field.

Query

Byte Name

Example RTU ASCII

Start frame

„:“ 0x3A

Slave address

11 0x0B „0B“ 0x30, 0x42

Function code

2 0x02 „02“ 0x30, 0x32

Start address high

0 0x00 „00“ 0x30, 0x30

Start address low

0 0x00 „00“ 0x30, 0x30

Count high

0 0x00 „00“ 0x30, 0x30

Count low

10 0x0A „10“ 0x31, 0x30

Error Check

LRC / CRC

0xF8

0xA7

„E3“ 0x45, 0x33

End of frame

t1-t2-t3 CRLF 0xD, 0xA

Response

The Bus Terminal Controller answers with byte count 2, i.e. 2 bytes of data

are returned. The query was for 10 bits, and these are now distributed over

2 bytes. The first bit in the input process image of the BC7300 is set, and

the Bus Coupler returns a "1" in the first data byte.

Byte Name

Example RTU ASCII

Start frame

„:“ 0x3A

Slave address

11 0x0B „0B“ 0x30, 0x42

Function code

2 0x02 „02“ 0x30, 0x32

Byte Count

2 0x02 „02“ 0x30, 0x32

Data 0..7

1 0x01 „01“ 0x30, 0x31

Data 8..15

0 0x00 „00“ 0x30, 0x30

Error Check

LRC / CRC

0x20

0x29

„F0“ 0x46, 0x30

End of frame

t1-t2-t3 CRLF 0xD, 0xA

Read Analog In/Outputs (Function 3)

READ HOLDING

REGISTERS

Function 3 can be used to read the input and output words and the

registers.

In this example the first two analog outputs of slave number 11 are read.

The analog outputs begin at offset 0x800 (hex). The length indicates the

number of channels to be read.

From Firmware B4 reading with function 3 is allowed.

1 2 ... 23 24 25 26 27 28 29 30 31 32 33 ... 47 48

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Beckhoff BC7300 Manuel d'utilisateur Page 28

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