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VFD68 Variable Frequency Drives
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Message Frame (Protocol)
Communication Method
The master sends a query message (question), and the slave returns a response message (response). When
communication is normal, Device Address and Function Code are copied. When communication is abnormal
(function code or data code is illegal), bit 7 (=80H) of Function Code is turned on, and the error code is set to
Data Bytes.
The message frame consists of the four message fields as shown in Figure 57. By adding the no-data time
(T1: Start, End) of 3.5 characters to the beginning and end of the message data, the slave recognizes it as one
message.
Protocol Details
Table 89: Summary of Message Fields
Start
1
2
3
4
End
Address
Function
Data
CRC Check
T1
8 bit
8 bit
n x 8 bit
L 8 bit
H 8 bit
T1
Table 90: Description of Message Fields (Part 1 of 2)
Message
Field
Description
Address
The address code is 1 byte long (8 bits) and any address from 0 to 247 can be set. Set 0 to send a
broadcast message (all-address instruction) or any of 1 to 247 to send a message to each slave.
When the slave responds, it returns the address set from the master.
The value of P.117 is the slave address.
Device Address
Function Code
Eight-Bit
Data Bytes
Error Check
Device Address
Function Code
Eight-Bit
Data Bytes
Error Check
Query Message
from Master
Response Message
from Slave
Figure 57: Communication Message Structure