INVT Goodrive350 Series Operation Manual page 316

Goodrive350 IP55 High-ingress Protection Series VFD Communication protocol
the data receiving device cannot identify data errors and may make an incorrect response. The
incorrect response may cause severe problems. Therefore, the data must be checked.
The check is implemented as follows: The transmitter calculates the to-be-transmitted data
based on a specific algorithm to obtain a result, adds the result to the rear of the message, and
transmits them together. After receiving the message, the receiver calculates the data based
on the same algorithm to obtain a result, and compares the result with that transmitted by the
transmitter. If the results are the same, the message is correct. Otherwise, the message is
considered incorrect.
The error check of a frame includes two parts, namely, bit check on individual bytes (that is,
odd/even check using the check bit in the character frame), and whole data check (CRC
check).
Bit check on individual bytes (odd/even check)
You can select the bit check mode as required, or you can choose not to perform the check,
which will affect the check bit setting of each byte.
Definition of even check: Before the data is transmitted, an even check bit is added to indicate
whether the number of "1" in the to-be-transmitted data is odd or even. If it is even, the check
bit is set to "0, and if it is odd, the check bit is set to "1".
Definition of odd check: Before the data is transmitted, an odd check bit is added to indicate
whether the number of"1" in the to-be-transmitted data is odd or even. If it is odd, the check bit
is set to"0",; and if it is even, the check bit is set to"1",
For example, the data bits to be sent are "11001110", including five "1". If the even check is
applied, the even check bit is set to "1"; and if the odd check is applied, the odd check bit is set
to "0". During the transmission of the data, the odd/even check bit is calculated and placed in
the check bit of the frame. The receiving device performs the odd/even check after receiving
the data. If it finds that the odd/even parity of the data is inconsistent with the preset
information, it determines that a communication error occurs.
Cyclic redundancy check (CRC)
A frame in the RTU format includes an error detection domain based on the CRC calculation.
The CRC domain checks all the content of the frame. The CRC domain consists of two bytes,
including 16 binary bits. It is calculated by the transmitter and added to the frame. The receiver
calculates the CRC of the received frame, and compares the result with the value in the
received CRC domain. If the two CRC values are not equal to each other, errors occur in the
transmission.
During CRC, 0xFFFF is stored first, and then a process is invoked to process a minimum of 6
contiguous bytes in the frame based on the content in the current register. CRC is valid only for
the 8-bit data in each character. It is invalid for the start, stop, and check bits.
During the generation of the CRC values, the "exclusive or" (XOR) operation is performed on
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