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Chapter 4 Parameters｜VFD-EL-W

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(1) ASCII mode (LRC Check):

LRC (Longitudinal Redundancy Check) is calculated by summing up the values of the bytes

from ADR1 to the last data character then calculating the hexadecimal representation of the 2’s-

complement negation of the sum. Take the above 3.3.1 Command Message for example: 01H +

03H + 21H + 02H + 00H + 02H = 29H, take complementary number of 2 = D7H

LRC (Longitudinal Redundancy Check) is calculated from Address to Data content. It is

calculated by the following steps:

Step 1: Load a 16-bit register (called CRC register) with FFFFH.

Step 2: Exclusive OR the first 8-bit byte of the command message with the low order byte of the

16-bit CRC register, and put the result in the CRC register.

Step 3: Examine the LSB of CRC register.

Step 4: If the LSB of CRC register is 0, shift the CRC register one bit to the right, fill MSB with

zero, then repeat step 3. If the LSB of CRC register is 1, shift the CRC register one bit

to the right, fill MSB with zero, Exclusive OR the CRC register with the polynomial value

A001H, then repeat step 3.

Step 5: Repeat step 3 and 4 until you perform eight shifts. This processes a complete 8-bit byte.

Step 6: Repeat step 2 through 5 for the next 8-bit byte of the command message. Continue

doing this until all bytes are processed. The final contents of the CRC register are the

CRC value. When transmitting the CRC value in the message, the upper and lower

bytes of the CRC value must be swapped, that is, the lower order byte is transmitted

first.

The following is an example of CRC generation using C language. The function takes two

arguments:

Unsigned char* data  a pointer to the message buffer

Unsigned char length  the quantity of bytes in the message buffer

The function returns the CRC value as a type of unsigned integer. Unsigned int

crc_chk(unsigned char* data, unsigned char length)

{

int j;

unsigned int reg_crc=0xffff;

while(length--){

reg_crc ^= *data++;

for(j=0;j<8;j++){

if(reg_crc & 0x01){ /* LSB(b0)=1 */

reg_crc=(reg_crc>>1) ^ 0xa001;

}else{

reg_crc=reg_crc >>1;

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