Jaden DLB1-0004T4G, Инструкция по эксплуатации

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7.2 Verification mode
CRC mode:CRC (Cyclical Redundancy Check) uses RTU frame format message,
includes error detection method based on CRC fields. CRC field detects the entire
contents of the message. CRC field includes two bytes, and contains a 16-bit binary value.
It adds to the message after calculations from the transmission equipment. The receiver
recalculates the received CRC messages, and compares with CRC value in the domain. If
the two CRC values do not equal, then the transmission has errors.
CRC firstlydeposits 0xFFFF, then calls a consecutive 8-bit bytes in the message and
processes with the value currently in the registry. Only 8-bit data from each character is
valid for CRC; start and stop bits, and parity bit are invalid.
In CRC process, each 8-bit word XOR with registry separately. The result moves to
the lowest valid place. Highest valid place is 0. If LSB is 1, registry value will XOR with
preset values separately; if LSB is 0, then not execute. The whole process will repeat 8
times. When the last one (8th bit) completes, next 8-bit byte will start XOR with current
value.CRC value is the value in the registry after all bytes are processed.
When adding CRC to a message, low byte adds first, then the high byte.
CRC calculation programs:
unsigned int cal_crc16 (unsigned char *data, unsigned int length)
{
unsigned int i, crc_result=0xffff;
while(length--)
{
crc_result^=*data++;
for(i=0; i<8; i++)
{
if(crc_result&0x01)
crc_result=(crc_result>>1)^0xa001;
else
crc_result=crc_result>>1;
}
}
crc_result=((crc_result&0xff)<<8)|(crc_result>>8);
return(crc_result);