Delta DVP-15MC Series, Operation Manual

Page: 909 / 972

Appendix A. Modbus Communication
A-5
A_
A.2 Message Format in RTU Mode

Communication data structure
Start
No input data for more than 10ms
Communication address
Slave address: 8-bit binary address
Function code
Function code: 8-bit binary address
Data (n-1)
Data content
n × 8 bit binary data, n<=202
…….
Data 0
Low byte of CRC check
CRC check sum
High byte of CRC check
End
CRC check sum is composed of two 8-bit binary data

Communication address
The range of a valid communication address is 0
～
254. The communication address 0 indicates
to broadcast the message to all slaves and the slaves which have received the broadcast
message do not make any response. If the communication address is not 0, slaves will reply to
master as normal. For example, to communication with the slave with the communication
address of 16, the address of the slave is set as 16#10 since decimal 16 is equal to hexadecimal
10.

Function code and data
The data format is determined by function codes.
For example, to read the data of two continuous addresses with 16#0000 as start address in
DVP-15MC series motion controller, the address of DVP-15MC is 1, 16#0000 is the Modbus
address of %MW0 in the controller.
The data in the communication cable and the explanation on them are shown below:
PC
→
DVP-15MC series motion controller: “01 03 00 00 00 02 C4 0B”
DVP-15MC series motion controller
→
PC: “01 03 04 00 01 02 00 2A 32”

Request message:
Field name Character
Start No input data for more than 10ms
Communication address
01
Function code
03
High byte of Modbus address
00
Low byte of Modbus address
00
Read high byte of data number
00
Read low byte of data number
02
Low byte of CRC check sum C4
High byte of CRC check sum
0B
End
No input data for more than 10ms