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VFD68 Variable Frequency Drives Technical Bulletin
Product
Document type
Technical Bulletin
Document revision
C
Revision date
2019-08-09
Part number
24-7664-3051
Table 1. 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 2. Description of Message Fields
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 subordinate.

When the subordinate responds, it returns the address set from the master.

The value of P.117 is the subordinate address.
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 subordinate, and the subordinate 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 subordinate returns an error response.
  • When the subordinate returns a normal response, it returns the function code set by the master.
  • When the subordinate 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 subordinate 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 subordinate flags this message as containing an error and discards the message.