Goodrive18 series two-in-one VFD Communication
-116-
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 sender 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
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 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
Summary of Contents for GD18-004-4-2
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