BECKHOFF BK7300 - Manual (Page 31)

MODBUS
BK7300 27
Writing a Number of Analogue Outputs (Function 16)
PRESET MULTIPLE
REGISTERS Function 16 can be used to write a number of analogue outputs. In this
example the first 2 analogue output words of slave number 11 are written.
The analogue 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 analogue 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.
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 coupler 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