VFD68 Variable Frequency Drives
95
Function
The function code is 1 byte (8 bits) and any address from 0 to 247 can be set. The master sets the
function that it wants to request to the slave, and the slave performs the requested operation.
See the sub-table for the supported function codes.
Code
Function Name
Outline
Broadcast
Communication
H03
Read Holding Register
Reads the holding register
data
Not Allowed
H06
Present Single Register
Writes data to the holding
register
Allowed
H08
Diagnostics
Function diagnosis
(communication check only)
Not Allowed
H10
Present Multiple Register
Writes data to multiple
consecutive holding registers
Allowed
H46
Read Holding Register Access Log
Reads the number of registers
that succeeded in
communication last time
Not Allowed
•
If the set function code is other than the ones listed in this sub-table, the slave returns an error
response.
•
When the slave returns a normal response, it returns the function code set by the master.
•
When the slave returns an error response, it returns H80 + function code.
Data
The format changes depending on the function code. Data includes the byte count, number of bytes,
description of the access to the holding register, and similar information.
CRC Check
The message frame is checked for error by creating a CRC number. This two-byte long CRC data is
added to the end of the message. When CRC is added to the message, the low-order byte is added first
and is followed by the high-order byte.
The CRC value is calculated by the master and is added to the master message. The slave recalculates
the CRC after the message is received and compares it with the value received in the message. If these
values do not match, then the slave flags this message as containing an error and discards the
message.
Table 90: Description of Message Fields (Part 2 of 2)
Message
Field
Description
