FOTEK GD20-004G-2, Operation Manual

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Goodrive20 Series VFD Communication protocol
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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
low-order bit to the high-order bit, and 0 is placed in the high-order bit. Then, the low-order bit
is detected. If the low-order bit is 1, the XOR operation is performed on the current value in the
register and the preset value. If low-order bit 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 example 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;
} }
return(crc_value);
}
In the ladder logic, CKSM uses the table look-up method to calculate the CRC value according
to the content in the frame. The program of this method is simple, and the calculation is fast,
but the ROM space occupied is large. Use this program with caution in scenarios where there