BECKHOFF BC7300 - Manual (Page 33)

BC7300 33
Query
Byte Name Example RTU ASCII
Start frame „:“ 0x3A
Slave address 11 0x0B „0B“ 0x30, 0x42
Function code 16 0x10 „10“ 0x31, 0x30
Start address high 8 0x08 „08“ 0x30, 0x38
Start address low 0 0x00 „00“ 0x30, 0x30
Length high 0 0x00 „00“ 0x30, 0x30
Length low 2 0x02 „02“ 0x30, 0x32
Byte Count 4 0x04 „04“ 0x30, 0x34
Data 1 byte 1 127 0x7F „7F“ 0x37, 0x46
Data 1 byte 2 255 0xFF „FF“ 0x46, 0x46
Data 2 byte 1 63 0x3F „3F“ 0x33, 0x46
Data 2 byte 2 255 0xFF „FF“ 0x46, 0x46
Error Check
LRC / CRC
0xCD
0xE3 „1B“ 0x31, 0x42
End of frame t1-t2-t3 CRLF 0xD, 0xA
Response
The Bus Terminal Controller replies with the start address and the length of
the transmitted words.
Byte Name Example RTU ASCII
Start frame „:“ 0x3A
Slave address 11 0x0B „0B“ 0x30, 0x42
Function code 16 0x10 „10“ 0x31, 0x30
Start address high 8 0x08 „08“ 0x30, 0x38
Start address low 0 0x00 „00“ 0x30, 0x30
Length high 0 0x00 „00“ 0x30, 0x30
Length low 2 0x02 „02“ 0x30, 0x32
Error Check
LRC / CRC
0x43
0x02 „DB“ 0x44, 0x42
End of frame t1-t2-t3 CRLF 0xD, 0xA
Writing and Reading Analog Outputs and Inputs
(Function 23)
READ / WRITE
REGISTERS
A number of analog outputs can be written and a number of analog inputs
read with one telegram using function 23. In this example the first 2 analog
output words of slave number 11 are written, and the first two analog inputs
are read. The analog outputs start at offset 0x0800 (hex), while the inputs
start at offset 0x0000 (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 0x3FFF
(hex), and the second word is to receive the value 0x7FFF.