Brian Marshall

Important changes to forums and questions

All forums and questions are now archived. To start a new conversation or read the latest updates go to forums.mbed.com.

5 years, 1 month ago.

I2C & EEPROM

Can anyone tell me how use the I2C API with an EEPROM. I'm using the 24AA64F, and I can't figure it out.

I think I understand how the 24AA64F expects to be addressed, but I'm having a hard time understanding the API.

The hello world sketch is for something completely unrelated, and seems to have an unused variable 

const int addr7bit = 0x48;      // 7 bit I2C address

I don't know if this is an error, or just an indicator that I'm completely missing something.

This is code I wrote months ago, which I thought worked. It does something, but I don't think it's communicated with the eeprom at all. 

#include "mbed.h"
I2C i2c(I2C_SDA, I2C_SCL );
int readVariable;
int address = 0xa1;
char array[1] ;
char arrayRead[1];
int main()
{
    while (1) {
        array[1] = 0x07;        // just a random number
        i2c.start();
        i2c.write(address,array,1);     //write to address
        i2c.read(address,arrayRead,1);  //read from address
        i2c.stop();
        wait(.01);
        
        readVariable = arrayRead[0];        
        printf("variable = %i\r\n", readVariable);
        wait(1);
        }
 }

2 Answers

Paul Staron
5 years, 1 month ago.

You could have a look here:

https://os.mbed.com/users/bborredon/code/eeprom/file/925096a4c7f0/eeprom.h/

I use this for 24Cxxx series, it may work the same for yours with modifications to the addressing.

I believe the 24Axxx eeproms are compatible, but can operate at a lower voltage. I tried a couple libraries, but don't think I tried this one.

One I did try https://os.mbed.com/users/rhourahane/code/I2CEeprom/ I was getting compile errors just from initializing the class

	I2CEeprom (PinName sda, PinName scl, int address, size_t pageSize, size_t chipSize, int busSpeed=400000)

I set the values appropriately as far as i could tell, but the compiler was telling me it wanted closing parentheses after the SDA pin name.

I'll take a look at eeprom.h. thanks.

posted by Brian Marshall 09 Mar 2019
Jan Kamidra
5 years, 1 month ago.

Hi, I see two problems. The i2c and array are used incorrectly.

The start and stop are already included in these methods. And you can printf results

I2c

       // i2c.start();
       result_write = i2c.write(address,array,1);     //write to address
       printf("write = %d\n", result_write);
       result_read =  i2c.read(address,arrayRead,1);  //read from address
       printf("read= %d\n", result_read);
       // i2c.stop();

Please see documentation https://os.mbed.com/docs/mbed-os/v5.11/apis/i2c.html#a37956c174106ecc64cae8f87dcf9fc7a

Array

   char array[1] ;          // an array with one char
   array[1] = 0x07;        //it start form zero so position 1 is out of range and your i2c.write always write empty position 0
   array[0] = 0x07;         //correct

Please see documentation http://www.cplusplus.com/doc/tutorial/arrays/