Putting a signed integer into external EEPROM

Projects Programming
1

Hi guys, so for my project since I need quite a bit of memory I'm placing my data into an external EEPROM, I have everything set up fine using example code from http://www.hobbytronics.co.uk/arduino-external-eeprom which is great but I want to place a Unix Epoch value into the EEPROM and I don't think it will fit with the code from that site and I think the largest value I get is 256. I've been trying to use the example code from here Arduino Playground - EEPROMReadWriteLong but since I'm using an external EEPROM with I2C I think it is? It uses Wire.write instead of EEPROM write, and I'm unsure if its okay for me to send 4 writes in a row or whether I can just change those EEPROM writes to wirewrites. I don't really understand the whole shifting bit either which makes it sort of difficult as well.

If it helps I'm using the 24lc256 EEPROM

2

It's that easy, use the Wire.write()s to your EEPROM instead of the EEPROM.write() you see in the playground article. You can eliminate some code if you do a sequential write:

void writeEEPROM(int deviceaddress, unsigned int eeaddress, uint32_t data ) 
{
  Wire.beginTransmission(deviceaddress);
  Wire.write((int)(eeaddress >> 8));   // MSB
  Wire.write((int)(eeaddress & 0xFF)); // LSB
  Wire.write(data & 0xff);
  Wire.write((data >> 8) & 0xff);
  Wire.write((data >> 16) & 0xff);
  Wire.write((data >> 24) & 0xff);
  Wire.endTransmission();
}

or a bit faster:

void writeEEPROM(int deviceaddress, unsigned int eeaddress, uint32_t data ) 
{
  Wire.beginTransmission(deviceaddress);
  Wire.write((int)(eeaddress >> 8));   // MSB
  Wire.write((int)(eeaddress & 0xFF)); // LSB
  uint i;
  for (i = 0; i < 4; i++) {
    Wire.write(data & 0xff);
    data >>= 8;
  }
  Wire.endTransmission();
}
3

Thanks heaps mate, that helped me out a lot, especially since i had some code to look at as well, I'm trying to get the reading part done too but I seem to be having a bit of problems with that as well. I attempted the following code:

long EEPROMReadlong(int deviceaddress, unsigned int address )
{
  Wire.beginTransmission(deviceaddress);
  Wire.write((int)(address >> 8));   // MSB
  Wire.write((int)(address & 0xFF)); // LSB

  //Read the 4 bytes from the eeprom memory.
  long four = Wire.read(address);
  long three = Wire.read(address + 1);
  long two = Wire.read(address + 2);
  long one = Wire.read(address + 3);

  //Return the recomposed long by using bitshift.
  return ((four << 0) & 0xFF) + ((three << 8) & 0xFFFF) + ((two << 16) & 0xFFFFFF) + ((one << 24) & 0xFFFFFFFF);
}

Which is pretty much just changing the eeprom.read to wire.read() but I keep getting an error saying that no matching function call to TwoWire::Read(unsinged int&). I'm assuming it has something to do with the unsigned int address but since I used that in the write I don't quite understand why it doesn't work here?

Also if I write to address 1 in the code from what I understand it writes the long over address 1, 2, 3 and 4 right? So If I wanted to store another long value, I should place it at address 5 right? and not at 2 since then it will rewrite over 2, 3, 4 and also write 5?

----------edit--
Okay so I had another go at it with the following reading code:

long EEPROMReadlong(int deviceaddress, unsigned int address )
{
  long four, three, two, one;
  Wire.beginTransmission(deviceaddress);
  Wire.write((int)(address >> 8));   // MSB
  Wire.write((int)(address & 0xFF)); // LSB

  //Read the 4 bytes from the eeprom memory.
  Wire.requestFrom(deviceaddress, address);
  if (Wire.available()) four = Wire.read();

  Wire.requestFrom(deviceaddress, (address + 1));
  if (Wire.available()) {
    three = Wire.read();
  }
  Wire.requestFrom(deviceaddress, (address + 2));
  if (Wire.available()) {
    two = Wire.read();
  }
  Wire.requestFrom(deviceaddress, (address + 3));
  if (Wire.available()) {
    one = Wire.read();
  }
  //Return the recomposed long by using bitshift.
  return ((four << 0) & 0xFF) + ((three << 8) & 0xFFFF) + ((two << 16) & 0xFFFFFF) + ((one << 24) & 0xFFFFFFFF);
}

But unfortunately it doesn't print anything on the screen when I call

void setup()
{
  Wire.begin(); 
  Serial.begin(57600); 
  Serial.print("init");
  delay(5000);
  for (int i = 0; i < 10000; i += 4)
  {
    Serial.println(EEPROMReadlong(disk1, i));
    delay(10);
  }
}
4

You haven't understood, how I2C works. Try this version:

long EEPROMReadlong(int deviceaddress, unsigned int address )
{
  long four, three, two, one;
  Wire.beginTransmission(deviceaddress);
  Wire.write((int)(address >> 8));   // MSB
  Wire.write((int)(address & 0xFF)); // LSB
  if (Wire.endTransmission()) return -1;

  //Read the 4 bytes from the eeprom memory.
  if (Wire.requestFrom(deviceaddress, 4) == 4) {
    uint8_t i;
    uint32_t v = 0;
    for (i = 0; i < 4; i++) {
      uint32_t r = Wire.read();
      v |= r << ((3-i) * 8);
    }
    return v;
  } else {
    return -1;
  }
}