INVT Goodrive390L Series User Manual page 70

Goodrive390L Series Lift-Dedicated VFD
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 the each 8-bit character and the content in the register. The result is placed in the
bits from the least significant bit (LSB) to the most significant bit (MSB), and 0 is placed in
the MSB. Then, LSB is detected. If LSB is 1, the XOR operation is performed on the current
value in the register and the preset value. If LSB is 0, no operation is performed. This
process is repeated for 8 times. After the last bit (8th bit) is detected and processed, the
XOR operation is performed on the next 8-bit byte and the current content in the register.
The final values in the register are the CRC values obtained after operations are
performed on all the bytes in the frame.
The calculation adopts the international standard CRC check rule. You can refer to the
related standard CRC algorithm to compile the CRC calculation program as required.
The following example is a simple CRC calculation function for your reference (using the
C programming language):
unsigned
data_length)
{
int i;
unsigned int crc_value=0xffff;
while(data_length--)
{
crc_value^=*data_value++;
202403 (V1.0）
int crc_cal_value(unsigned
Communication protocol
char*data_value,unsigned char
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