Read/Write to/from EEPROM

Using Arduino Programming Questions
1

I want to add an external EEPROM to store some simple values between 0 and 255. I'm using an AT24C256 external EEPROM board. So for example, I want to specify memory space 1, and store, say 217. Memory space 2, store the number 45. I found the following sketch, and I'm getting errors, which I can see why, but not sure how to correct them. It's saying "writeI2CByte was not declared in this scope." I'm not sure how to declare it.

As a side note, I added MODE and the subsequent if statement for it. This is just for testing purposes so it's not constantly writing to the EEPROM.

I'm sure there's other errors, and I might also be whizzing up the wrong tree in the first place altogether.

#include <Wire.h>
#define ADDR_Ax 0b000 //A2, A1, A0
#define ADDR (0b1010 << 3) + ADDR_Ax
int MODE;

void setup() {
  Serial.begin(9600);
  Wire.begin();
  writeI2CByte(0, 1);
  Serial.println(readI2CByte(0));
  MODE=1;
}

void loop() {  

if (MODE ==1){
void writeI2CByte(byte data_addr, byte data){
  Wire.beginTransmission(ADDR);
  Wire.write(1);
  Wire.write(217);
  Wire.endTransmission();
  MODE = 2;
  delay(50);
}
}
byte readI2CByte(byte data_addr){
  byte data = NULL;
  Wire.beginTransmission(ADDR);
  Wire.send(1);
  Wire.endTransmission();
  Wire.requestFrom(ADDR, 1); //retrieve 1 returned byte
  delay(15);
  if(Wire.available()){
    data = Wire.read();
  }
  return data;
  Serial.println(data);
}
2

Put out the function definition out of the loop().

1 Like
3

A program is a list of definitions, but function definitions only allowed at top level, so not inside loop() - this is a quirk of C and C++.

4

The function definition is outside the loop(), but the code is very badly indented.

5

No.
The definition is inside the if inside the loop.

6

Yes you are right!
I've missed the second function definition... :sweat_smile:

7

Hi @tpaairman

try this:

#include <Wire.h>
#define ADDR_Ax 0b000 //A2, A1, A0
#define ADDR (0b1010 << 3) + ADDR_Ax
int MODE;

void setup() {
  Serial.begin(9600);
  Wire.begin();
  writeI2CByte(0, 1);
  Serial.println(readI2CByte(0));
  MODE = 1;
}

void loop() {

  if (MODE == 1)
  {
     //????????????
  }
}
  void writeI2CByte(byte data_addr, byte data) 
  {
    Wire.beginTransmission(ADDR);
    Wire.write(1);
    Wire.write(217);
    Wire.endTransmission();
    MODE = 2;
    delay(50);
  }

  byte readI2CByte(byte data_addr) 
  {
    byte data = NULL;
    Wire.beginTransmission(ADDR);
//    Wire.send(1);       ///  send ????????
    Wire.endTransmission();
    Wire.requestFrom(ADDR, 1); //retrieve 1 returned byte
    delay(15);
    if (Wire.available()) {
      data = Wire.read();
    }
    return data;
    Serial.println(data);
  }
8

So, this is a sketch that you have not created. Why not you try to create your own sketch from the following tips to write/read data byte 0x23 into/from location 0x1234?

1. Build connection diagram between UNo and EEPROM as per Fig-1 given below.

eepromAT24C256
Figure-1:

2. Upload the following sketch in UNO.

#include<Wire.h>
byte myData = 0x23;  //data byte to be stored at location 0x1234 of EEPROM
int eepromAddress = 0x1234;  //EEPROM location that will hold data byte 0x23

void setup()
{
  Serial.begin(9600);
  Wire.begin();
  //--- wrieitng 0x23 at location address 0x1234
  Wire.beginTransmission(0x50); //EEPROM's i2C address
  Wire.write(highByte(eepromAddress));  //pointing beginning address of EEPROM
  Wire.write(lowByte(eepromAddress));
  Wire.write(myData); 
  byte busStatus = Wire.endTransmission();
  if (busStatus != 0)
  {
    Serial.print("EEPROM is not found...!");
    while (1);  //wait for ever
  }
  Serial.println("EEPROM is found.");
  delay(5); //write cycle delay
  //---reading back the data--------------
  Wire.beginTransmission(0x50);
  Wire.write(highByte(eepromAddress));  //pointing target location address of EEPROM
  Wire.write(lowByte(eepromAddress));
  Wire.endTransmission();
  //--------------------------------------------
  byte n = Wire.requestFrom(0x50, 1); //reading 1 bytes data from location 0x1234
  byte recData = Wire.read();
  Serial.print(recData, HEX); //Serial Monitor should show: 23
}

void loop()
{

}
9

After looking into things further, I found info to put me on the right track. Being new to all of this, I didn't catch that I needed to define the operation in the setup and not the loop. But I'm now able to write and read to the EEPROM.

10

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