hello everybody, iam doing final year project. In that i have to write some data into and read from a EEPROM using I2C protocol. iam using atmel's AT24C04 (4K) EEPROM and AT89s52 controller. I have interfaced the EEPROM using pins P1.0(SCL) and P1.1 (SDA) of thee eeprom.
i have written the code in c language. but when i tested it with pinnacle 52 proffessional development system (evaluation version). iam getting this kind of output on the i2c bus 1 device

[START][Addr:50-Write]<ACK>[00]<ACK>[AA]<ACK>[STOP]
[START][Addr:50-Write]<ACK>[00]<ACK>
[START][Addr:50-Read]<ACK><00>[NAK]<00>

but when i check the device in pinnacle there all all zero's in the required memory location. my data that i have written into the required address has not been written and the same data is not being read from it. i have given a device address of 0xA0 but int he above output iam getting 50. i could not understand why it is so.

iam attaching mycode here can anyone please help me in this regard.

#include<reg52.h>
#include <intrins.h> // includes _nop_(); function

sbit SCL = P1^0;
sbit SDA = P1^1;

void i2cstart(void);
bit i2cstop();
bit i2cdatawrite(unsigned int );
unsigned int i2cdataread(void);

void main()
{
unsigned int value;
SDA = 0;
SCL = 0;
i2cstart();
value = 0xA0; // device address
i2cdatawrite(value);
value = 0x00; // data word address
i2cdatawrite(value);
value = 0xAA; // byte to be written
i2cdatawrite(value);
i2cstop();
P2 = i2cdataread();

}


void i2cstart()
{
SDA = 1; //data has to be high before the clock
//is, this is the definition of a start
SCL = 1;
_nop_();
SDA= 0; //change the data while CLK is high
_nop_();
SCL = 0;
}


bit i2cstop()
{

unsigned char retry = 9;

SDA = 1; // set it high so we can use it as an input
while (retry--)
if (!SDA) // while the data line is low
{ // continue to pulse the clock
SCL= 1;
_nop_();
SCL = 0;
}
else
{ // when the data line actually is high
SDA = 0; // we can now execute a valid STOP
_nop_();
SCL = 1;
_nop_();
SDA = 1;
return(1);
}
SCL = 1;
return (0); // stop state has failed.

}

bit i2cdatawrite(unsigned int byte_to_send)
{
unsigned char bit_pos;
bit ack;
SCL = 0;
for(bit_pos = 0x80; bit_pos != 0; bit_pos >>= 1) // MSB first
{
if (byte_to_send & bit_pos)
SDA = 1;
else
SDA = 0;

SCL = 1;
_nop_();
SCL= 0;
}

/*--- now get the "ack" bit to make sure everything is good ---*/
SDA = 1; // set for input
_nop_();

SCL = 1; // data can be read when the clock is high
_nop_();
ack = SDA; // read the ack bit
SCL = 0;

return(ack == 0);// returning ACK bit, an I2C ACK is a 0, so we'll
// change it to positive logic to make it easier
}


unsigned int i2cdataread(void)
{
unsigned int x = 0x00,value;
unsigned char index;
i2cstart();
value = 0xA0; // device address
i2cdatawrite(value);
value = 0x00; // data word address
i2cdatawrite(value);
value = 0xA1; // device address with R/W = 1;
i2cstart();
i2cdatawrite(value);
SDA = 1; // set for a read

for(index = 0x80; index != 0; index >>= 1) // MSB first
{
_nop_();
SCL = 1;
if (SDA)
x |= index;
SCL = 0;
}

SDA = 1; // ACK (0) or NACK (1) bit
_nop_();
SCL= 1;
_nop_();
SCL = 0;

return(x);
}


please tell me what the problem is, iam falling short of time.
thanks in advance
narender