Grow GM66 - 8. Serial Port Instructions and Zone Bits; 8.1 CRC Algorithm

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8 Serial Port Instruction
Users can settle the module by sending instruction from mainframe.
Please make sure communicate parameter complete matching between module and mainframe.
Module default serial communicate parameter: Baud rate 9600bps; No check; 8 bit data; 1 bit stop
bit; No flow control.
8.1CRC Algorithm
CRC: CRC_CCITT check value (2 bytes).
Suitable for Types、Lens、Address、Datas;
Characteristic polynomial : X16+X12+X5+1, multinomial coefficient: 0x1021, original value:0 ;
For single byte, the highest bit will be calculated at first, output will be without negation.
Reference code of C:
unsigned int crc_cal_by_bit(unsigned char* ptr, unsigned int len)
{
unsigned int crc = 0;
while(len-- != 0)
{
for(unsigned char i = 0x80; i != 0; i /= 2)
{
crc *= 2;
if((crc&0x10000) !=0)
crc ^= 0x11021;
if((*ptr&i) != 0)
crc ^= 0x1021;
}
ptr++;
}
return crc;
}
PS: when no need for checking CRC, CRC bite can be filled in 0xAB 0xCD