Arduino Forum

Using Arduino => Storage => Topic started by: gabomx on Mar 21, 2011, 06:39 pm

Title: Can't save data in Arduino EEPROM
Post by: gabomx on Mar 21, 2011, 06:39 pm
Hi.

Can't save data in my Arduino EEPROM. I've try with a MEGA 1280 and a Duemilanove: same results
I went back to basics (EEPROM READ - EEPROM WRITE)  and can't obtain results:
even with the example (loop write - read)
it seems work, but when i remove the write command, the result of my reading is 256 for every data.

Here is my code:
Code: [Select]


#include <EEPROM.h>
int a = 0;
int value;
int i;


void setup()
{
Serial.begin(9600);
for ( i = 0; i < 256; i++)     // 256  because it holds 1 byte only
{
   EEPROM.write(i, i);   // Write 0 in position 0, 1 in position 1 and so on
   delay(5);
   value = EEPROM.read(i);   //read position
  Serial.print(i);
  Serial.print("\t");
  Serial.print(value);
  Serial.println();
  delay(50);
// Result: serial monitor should appear : 0   0 / next line 1  1 ... /next line 256  256
}

}
void loop()
{
 

}

I hope anyone can helpme !!!  =(
Title: Re: Can't save data in Arduino EEPROM
Post by: robtillaart on Mar 21, 2011, 06:59 pm
HI Gabo,

(right forum this time ;)

The problem might be that EEPROM.write() uses two parameters and the value parameter should be a byte. - See http://www.arduino.cc/en/Reference/EEPROMWrite

You might cast the value like below.

Code: [Select]


#include <EEPROM.h>

int value;

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

for (int i = 0; i < 256; i++)     // 256  because it holds 1 byte only (BUT STILL IS AN INT!!)
{
   EEPROM.write(i, [color=red](byte)[/color] i);   // Write 0 in position 0, 1 in position 1 and so on
}

delay(100);

for (int i = 0; i < 256; i++)     // 256  because it holds 1 byte only
{
  value = EEPROM.read(i);      //read position
  Serial.print(i);
  Serial.print("\t ");
  Serial.println(value);
}
}
void loop() {}
Title: Re: Can't save data in Arduino EEPROM
Post by: PaulS on Mar 21, 2011, 07:05 pm
Look at the EEPROM::write() function. Notice, in particular, what the type of the 2nd argument is. Then, compare that to the types of the arguments that you provide.

If you were to call the function with the correct type of argument, you would get correct results.
Title: Re: Can't save data in Arduino EEPROM
Post by: johnwasser on Mar 21, 2011, 07:17 pm
Your sketch works fine for me on a Diecimila.  I upload the sketch, run it, see the expected output, comment out the write line, re-upload it, re-run it and see the same output.

Are you using something other then the IDE and USB port to upload your sketch?  Perhaps and Flash and EEPROM are being cleared as part of the upload.
Title: Re: Can't save data in Arduino EEPROM
Post by: AWOL on Mar 21, 2011, 07:19 pm
Quote
but when i remove the write command, the result of my reading is 256 for every data.

That's pretty remarkable.
Title: Re: Can't save data in Arduino EEPROM
Post by: gabomx on Mar 21, 2011, 07:34 pm
I'm using the sparfun's AVR pocket programming...

I'll try using the USB.
Title: Re: Can't save data in Arduino EEPROM
Post by: retrolefty on Mar 21, 2011, 08:39 pm

Look at the EEPROM::write() function. Notice, in particular, what the type of the 2nd argument is. Then, compare that to the types of the arguments that you provide.

If you were to call the function with the correct type of argument, you would get correct results.


If that is the root of the problem, then part of the blame might be the example sketch used in the Arduino reference section for EEPROM:

http://arduino.cc/en/Reference/EEPROMWrite

Code: [Select]
Example
#include <EEPROM.h>

void setup()
{
 for (int i = 0; i < 512; i++)
   EEPROM.write(i, i);
}

void loop()
{
}



And I ran the OP's sketch and it seemed to work fine writing to eeprom, and later after commenting out the writting to eeprom, still held and printed valid data from the eeprom.

Lefty
Title: Re: Can't save data in Arduino EEPROM
Post by: gabomx on Mar 21, 2011, 09:02 pm
I upload the sketch using the bootloader instead the Pocket programmer and it works fine.

then, the pocket programmer clears the IC and rewrites it????

The example works fine but it's incorrect.
Then I have to tear apart the value (integer)  in two bytes to save... and when I need to retrieve the value I need to call both bytes and "paste them" ???

How to do that ????
Title: Re: Can't save data in Arduino EEPROM
Post by: johnwasser on Mar 21, 2011, 09:19 pm
Write 16 bit integer 'value' into i and i+1:

  EEPROM.write(i, value>>8);   // Write high byte
  EEPROM.write(i+1, value);  // Write low byte


Read 16-bit integer 'value' from i and i+1:

value = (EEPROM.read(i) << 8) | EEPROM.read(i+1);
Title: Re: Can't save data in Arduino EEPROM
Post by: AWOL on Mar 21, 2011, 09:23 pm
http://arduino.cc/en/Reference/HighByte
http://arduino.cc/en/Reference/LowByte