Newland NLS-HR1250-70, Руководство пользователя, Страница: 18 / 172

** Enter Setup
9 Exit Setup
Read Register
The read register command is used to read the contents of 1 to 256 contiguous registers in the scanner.
Syntax: {Prefix1} {Types} {Lens} {Address} {Datas} {FCS}
Prefix1 : 0x7E 0x00 (2 bytes)
Types : 0x07 (1 byte)
Lens : 0x01 (1 byte).
Address: 0x0000~0xFFFF (2 bytes), starting register address.
Datas : 0x00~0xFF (1 byte), number of registers to be read. When Datas=0x00, 256
contiguous registers are to be read.
FCS : CRC-CCITT checksum (2 bytes)
Computation sequence: Types+ Lens+Datas;
polynomial: X
16
+X
12
+X
5
+1(0x1021), initial value: 0x0000.
The following C language program is provided for reference.
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;
}