TNETX15AE datasheet(52/78 Pages) TI

52 / 78 page

TNETX15AE

ADDRESS-LOOKUP DEVICE

SPWS041A – AUGUST 1997 – REVISED OCTOBER 1997

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

PRINCIPLES OF OPERATION

EEPROM initialization/automatic loading (LOAD) (continued)

The last four bytes read by the automatic loader correspond to a 32-bit CRC value for the information stored

in the EEPROM. The CRC value is calculated by using the following callable C routine, which assumes that the

data to be examined is loaded into an array eeprom_data [ ]:

void ifexeeprom (char *cs)

{

long crc;

int k;

crc = 0xffffffffl;

for (k=0;k<=38;k++)

{

crcbyt (eeprom_data[k], &crc);

}

crc ^= 0xffffffffl;

eeprom_data[k++]=(int) ((crc >> 24) & 0x0ffl);

eeprom_data[k++]=(int) ((crc >> 16) & 0x0ffl);

eeprom_data[k++]=(int) ((crc >>

8) & 0x0ffl);

eeprom_data[k++]=(int) ((crc

) & 0x0ffl);

}

crcbyt (dat,crc)

int dat;

long *crc;

{

int i;

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

{

crcbit(dat>>7,crc);

dat = dat <<1;

}

crcbit (dat,crc)

int dat;

long *crc;

{

if ( (((*crc>>31) & 11)^((long)dat & 11)) ==1)

{

*crc ^= 0x02608edbl;

*crc = *crc <<1;

*crc |= 0x00000001l;

}

else

{

*crc = *crc <<1;

*crc &= 0xfffffffel;

}

In this example, the values for which the CRC is calculated are placed in the eeprom_data[] array from offset

0 to 38 (0x26). The routine crcbyt is called for each byte. The C routine then places the calculated CRC values

in the eeprom_data[] array at locations 39 to 42 (0x27 to 0x2A).

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