EEPROM values maxed out

Forum 2005-2010 (read only) Hardware Interfacing
1

I am trying to use the 24lc256 EEPROM to store data but I am having issues with it. The EEPROM keeps giving me FF, and it isn't just one EEPROM, i tested the three that I have and all of them give me the same result. The code I am using is bellow:

#include <Wire.h>        
#define eeprom 0x50    

void setup(void){
  Wire.begin();           
  Serial.begin(9600); 

  unsigned int address = 0;  
  for(address = 0; address<10; address++) writeEEPROM(eeprom, address, 3);

  for(address = 0; address<10; address++) {
     Serial.print(readEEPROM(eeprom, address), HEX); 
     Serial.print(", ");
  }
}

void loop(){
}

void writeEEPROM(int deviceaddress, unsigned int eeaddress, byte data ) {
  Wire.beginTransmission(deviceaddress);
  Wire.send((int)(eeaddress >> 8));  
  Wire.send((int)(eeaddress & 0xFF)); 
  Wire.send(data);
  Wire.endTransmission();
}

byte readEEPROM(int deviceaddress, unsigned int eeaddress ) {
  byte rdata = 0xFF;
  Wire.beginTransmission(deviceaddress);
  Wire.send((int)(eeaddress >> 8));
  Wire.send((int)(eeaddress & 0xFF));
  Wire.endTransmission();
  Wire.requestFrom(deviceaddress,1);
  if (Wire.available()) rdata = Wire.receive();
  return rdata;
}
2

Insert

delay(10);

as the last line of your writeEEPROM() function.

It takes some time for the eeprom to burn the data into the silicon, according to specs.

3

Yes, the delay is needed.

Also you should probably be casting to byte instead of int in your wire.send calls.

Lastly, you have pull-up resistors on SDA and SCL right?

Lastly, lastly, your device address assumes you have A0, A1 and A2 tied low. Do you actually have them tied low and not floating?

4

BTW, the "eeprom values are maxed out" because no byte was written to eeprom. Usually, a "virgin" eeprom has its bytes set to 0xFF.