LRI512 Просмотр технического описания (PDF) - STMicroelectronics

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LRI512

Memory TAG IC 512 bit High Endurance EEPROM 13.56MHz, ISO 15693 Standard Compliant with E.A.S.

STMicroelectronics 

LRI512

APPENDIX B

The CRC Error Detection Method

The Cyclic Redundancy Check (CRC) is calculat-

ed on all data contained in a message, from the

start of the Flags through to the end of Data. This

CRC is used from the VCD to the LRI512, and

from the LRI512 to the VCD.

Table 54. CRC Definition

CRC Type Length

ISO/IEC 13239 16 bits

CRC Definition

Polynomial

X16 + X12 + X5 + 1 = Ox8408

Direction

Backward

Preset

0xFFFF

Residue

0xF0B8

To add extra protection against shift errors, a fur-

ther transformation on the calculated CRC is

made. The One’s Complement of the calculated

CRC is the value attached to the message for

transmission.

For checking of received messages the two CRC

bytes are often also included in the re-calculation,

for ease of use. In this case, given the expected

value for the generated CRC is the residue of

F0B8h

CRC Calculation Example

This example in C language illustrates one method

of calculating the CRC on a given set of bytes

comprising a message.

C-Example to calculate or check the CRC16 according to ISO/IEC 13239

#define POLYNOMIAL0x8408// x^16 + x^12 + x^5 + 1

#define PRESET_VALUE0xFFFF

#define CHECK_VALUE0xF0B8

#define NUMBER_OF_BYTES4// Example: 4 data bytes

#define CALC_CRC1

#define CHECK_CRC0

void main()

{

unsigned int current_crc_value;

unsigned char array_of_databytes[NUMBER_OF_BYTES + 2] = {1, 2, 3, 4, 0x91, 0x39};

int

number_of_databytes = NUMBER_OF_BYTES;

int

calculate_or_check_crc;

int

i, j;

calculate_or_check_crc = CALC_CRC;

// calculate_or_check_crc = CHECK_CRC;// This could be an other example

if (calculate_or_check_crc == CALC_CRC)

{

number_of_databytes = NUMBER_OF_BYTES;

}

else // check CRC

{

number_of_databytes = NUMBER_OF_BYTES + 2;

}

current_crc_value = PRESET_VALUE;

for (i = 0; i < number_of_databytes; i++)

{

current_crc_value = current_crc_value ^ ((unsigned int)array_of_databytes[i]);

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

{

if (current_crc_value & 0x0001)

{

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