Goodrive350 IP55 High-ingress Protection Series VFD
Communication protocol
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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 transmitted 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.
CRC check mode
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, end, 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 8
times. After the last bit (8
th
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 is a simple CRC calculation function for your reference (using the C
programming language):
unsigned int crc_cal_value(unsigned char×data_value,unsigned char
data_length)
{
int i;
unsigned int crc_value=0xffff;
while(data_length--)
{
crc_value^=×dat+;
for(i=0;i<8;i++)
{
if(crc_value&0x0001)
crc_value=(crc_value>>1)^0xa001;
else
crc_value=crc_value>>1;
