LS Mecapion L7 A001, User Manual

Page: 147 / 222

6. Communication Protocol
6-3
6.2 Communication Protocol Base Structure
The communication of the L7 servo drive complies with the international standard MODBUS-
RTU protocol. For information about items not covered in this manual, refer to the following
standard. (Related standard: Modbus application protocol specification 1.1b, 2006.12.28)
Also, the concept of sending and receiving in this manual is based on the host.
6.2.1 Sending/Receiving Packet Structure
The maximum sending/receiving packet length of the MODBUS-RTU protocol is 256 bytes.
Make sure that the total length of the sending/receiving packet does not exceed 256 bytes.
The MODBUS-RTU communication mode requires space of at least 3.5 char between the
end of the previous packet and the beginning of the next packet as show in the following
image to distinguish packets.
to
Packet1 Packet2 Packet3
at least 3.5 char at least 3.5 char 4.5 char
(1) Sending Packet Structure
Additional
Address
Function
Code
Data Error Check
Bytes 0 1 2 . . n-1 n
Details Node ID Function Data . . CRC (MSB) CRC (LSB)
(2) Receiving Packet Structure
[Normal Response]
Additional
Address
Function
Code
Data Error Check
Bytes 0 1 2 . . n-1 n
Details Node ID Function Data . . CRC (MSB) CRC (LSB)
[Abnormal Response]
Additional
Address
Function
Code
Data Error Check
Bytes 0 1 2 3 4
Descripti
on
Node ID
F
0x80
Exception code CRC (MSB) CRC (LSB)