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I have an ESP32 controller and am using AT24C1024 for communication. In my code, I am trying to access an external EEPROM at positions writing data from 0 to 10000 position data is = '1'. However, when I read data from position '1', I sometimes get junk values, such as 0, 255, or old written values. I have already tried changing the clock speed with Wire.setClock(100000), and I have attempted multiple writes to that location, but these modifications did not resolve the issue.

#include <Wire.h>

#define EEPROM_ADDR 0x50  
#define SDA_PIN 21        
#define SCL_PIN 22        
#define DATA_LIMIT 10000   
#define VALUE 1   

void setup() {
  Serial.begin(115200);  
  // Wire.begin(SDA_PIN, SCL_PIN);  

  Wire.begin();        


  for (uint16_t i = 0; i < DATA_LIMIT; i++) {
    writeEEPROM(i, VALUE);  
  }

  for (uint16_t i = 0; i < DATA_LIMIT; i++) {
    uint8_t value = readEEPROM(i);
      Serial.print(i);
      Serial.print(" -> ");
      Serial.println(value);
    delay(30);
  }
  Serial.println("End");
}

void loop() {
}

void writeEEPROM(uint16_t memAddress, uint8_t data) {
  Wire.beginTransmission(EEPROM_ADDR);
  Wire.write((int)(memAddress >> 8));   
  Wire.write((int)(memAddress & 0xFF)); 
  Wire.write(data);                     
  uint8_t result = Wire.endTransmission();

  if (result != 0) {
    Serial.print("'W'- F : ");
  }
  delay(10);  
}


uint8_t readEEPROM(uint16_t memAddress) {
  Wire.beginTransmission(EEPROM_ADDR);
  Wire.write((int)(memAddress >> 8));   // MSB of memory address
  Wire.write((int)(memAddress & 0xFF)); // LSB of memory address
  Wire.endTransmission();
  
  Wire.requestFrom(EEPROM_ADDR, 1);
  if (Wire.available()) {
    return Wire.read();  
  }
  
  return 0;
}
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1 Answer 1

Reset to default
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Wire.beginTransmission(EEPROM_ADDR);

Although this code might work when you are addressing the first page of the memory, however if you read the datasheet carefully under the section of Device Addressing and Figure 7 Device Addressing.

|  1 |  0 |  1 |  0 |  0 | A1 | Pg | R/W |
  MSB                                LSB

The I2C addressing includes the memory page address bit and the status of A1 pin. So assuming A1 is 0 with internal pulldown or hardware unconnected, the correct addressing should be

Wire.beginTransmission((uint8_t)(EPROM_ADDR | (uint8_t) (dataAddress >> 16));

The Wire library itself will be responsible to convert the 7-bit I2C addressing to 8-bit I2C addressing and the R/W bit.

BTW, although code like Wire.write((int)(memAddress >> 8)); because the compiler might take care of it. But since Wire.write() take an argument of uint8_t as the parameter, so the casting should be (uint8_t) (memAddress >> 8) instead of (int) (memAddress >> 8).

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  • 1
    Since the range of memAddress is [0, 9999], the bits above 2^13 are all zero. So this cannot be the reason for the problem. Commented Sep 25, 2024 at 10:03
  • @thebusybee, datasheet (page 3) say memory is "internally organized as 512 pages of 256 bytes each". Commented Sep 25, 2024 at 10:16
  • Wire.beginTransmission((uint8_t)(EPROM_ADDR | (uint8_t) (dataAddress >> 16)); and (uint8_t) (memAddress >> 8) . I changed this configuration, this configuration is correct, but now also 0 to 10000 position write the data is '1' comming junk character (0, 255 and old data) ,approximately 9500 data only correct, another data has junk character Commented Sep 25, 2024 at 11:51
  • Did you make the change to the readEEPROM(uint16_t memAddress) accordingly and the Wire.requestFrom(EEPROM_ADDR, 1);? Commented Sep 25, 2024 at 12:02
  • 1
    "512 pages of 256 bytes" Yes, and 10000 bytes need 40 pages. So the page number calculated from memAddress will never change the most significant bit P0, which is always 0. Commented Sep 25, 2024 at 16:25

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