BECKHOFF BC7300 - Manual (Page 45)

BC7300 45
Query
Byte Name Example RTU Description
Slave address 11 0x0B
Function code 4 0x04
Start address high 0 0x00
Start address low 0 0x00
Count high 0 0x00
Count low 2 0x02 Number of data words
Error Check
LRC / CRC
0x71
0x61
End of frame t1-t2-t3
Response
The Bus Terminal Controller answers with byte count 4, i.e. 4 bytes of data
are returned. The query was for 2 input words, and these are now
distributed over 4 bytes.
Byte Name Example RTU Description
Start frame
Slave address 11 0x0B
Function code 4 0x04
Count byte 4 0x04 Number of data bytes
Data 1 high byte 0 0x00 Address %QB129
Data 1 low byte 56 0x38 Address %QB128
Data 2 high byte 63 0x3F Address %QB131
Data 2 low byte 11 0x0B Address %QB130
Error Check
LRC / CRC
0x80
0x7E
End of frame t1-t2-t3