Beckhoff BC7300, Manual

Page: 32 / 48

MODBUS
32 BC7300
Query
Byte Name Example RTU ASCII
Start frame „:“ 0x3A
Slave address 11 0x0B „0B“ 0x30, 0x42
Function code 15 0x0F „0F“ 0x30, 0x46
Start address high 0 0x00 „00“ 0x30, 0x30
Start address low
0 0x00 „00“ 0x30, 0x30
Length high 0 0x00 „00“ 0x30, 0x30
Length low 20 0x14 „14“ 0x31, 0x34
Byte Count 3 0x03 „03“ 0x30, 0x33
Data 1 bit 0..7
255 0xFF „FF“ 0x46, 0x46
Data 2 bit 8..15 255 0xFF „FF“ 0x46, 0x46
Data 3 bit 16..19 0 0x00 „00“ 0x30, 0x30
Error Check
LRC / CRC
0x01
0x95 „D1“ 0x44, 0x31
End of frame t1-t2-t3 CRLF 0xD, 0xA
Response
The Bus Terminal Controller answers with the same telegram.
Byte Name Example RTU ASCII
Start frame „:“ 0x3A
Slave address 11 0x0B „0B“ 0x30, 0x42
Function code 15 0x0F „0F“ 0x30, 0x46
Start address high
0 0x00 „00“ 0x30, 0x30
Start address low
0 0x00 „00“ 0x30, 0x30
Data high 0 0x00 „00“ 0x30, 0x30
Data low 20 0x14 „14“ 0x30, 0x34
Error Check
LRC / CRC
0xDA
0xB0 „D2“ 0x44, 0x32
End of frame t1-t2-t3 CRLF 0xD, 0xA
Writing a Number of Analog Outputs (Function 16)
PRESET MULTIPLE
REGISTERS
Function 16 can be used to write a number of analog outputs. In this
example the first 2 analog output words of slave number 11 are written.
The analog outputs begin at offset 0x0800 (hex). Here the offset always
describes a word. Offset 0x0003 writes to the fourth word in the output
process image. The length indicates the number of words, and the "Byte
count" is composed from the combination all the bytes that are to be
written.
Example: 4 words – correspond to a byte count of 8
The data bytes contain the values for the analog outputs. In this example,
two words are to be written. The first word is to receive the value 0x7FFF
(hex), and the second word is to receive the value 0x3FFF.