6. Communication Protocol
6-3
6.2 Communication Protocol Base Structure
The communication of the XDL-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: Mudbugs 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.
(1) Sending Packet Structure
Additional
Address
Functio
n 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]
Additiona
l Address
Functio
n Code
Data Error Check
Bytes 0 1 2 3 4
Descripti
on
Node ID
Function+
0x80
Exception code CRC (MSB) CRC (LSB)
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