AC70 VC CONTROL FREQUENCY INVERTER MANUAL
APPENDIX
136
a new frame. Similarly, if the interval between a new frame start-up and the former frame is smaller than 3.5 byte time,
the receiving equipment will think that it is the former one frame continuation. Because of the jumbled frame, finally
CRC checking value is incorrect, what leads to the communication mistake.
RTU frame’s standard structure:
Frame START
Transmission time of 3.5 bytes
Slave machine address
Communication address:
0
～
247(decimal)(0 is broadcast address)
Function code CMD
03H:read slave machine parameter
06H: write slave machine parameter
08H:circuit auto-detection
Data domain
DATA
（
N-1
）
…
DATA
（
0
）
parameter address, parameter number, parameter values ,
CRC CHK low-order
Detecting value:16 bit CRC check value
CRC CHK high-order
Frame ending
transmission time of 3.5 bytes
5.2 Order code and communication data description
5.2.1 Order code:03H, read N word (can continue reading 5 words at most)
For example:A frequency inverter who is slave machine with address 01 H and memory initial address 0101H(
［
E-01
］
)
reads 3 words continuously. Then the structure of that frame is described as follows:
RTU host machine order information
START
Transmission time of 3.5 bytes
Slave machine address
01H
Order code
03H
Start address high-order
01H
Start address low-order
01H
Data number high-order
00H
Data number low-order
03H
CRC CHK low-order
55H
CRC CHK high-order
F7H
END
Transmission time of 3.5 bytes
RTU Slave machine responding information (normal)
START
Transmission time of 3.5 bytes
Slave machine address
01H
Order code
03H
Byte number low-order
06H
Data address 0101H high-order
00H
Data address 0101H low-order
02H
Data address 0102H high-order
00H
Data address 0102H low-order
00H
Data address 0103H high-order
00H
Data address 0103H low-order
06H
CRC CHK low-order
D8H
CRC CHK high-order
B7H
END
Transmission time of 3.5 bytes