# 5. EEPROM（电擦除存储器）

EEPROM的用法同Arduino UNO一样，分为读和写两种操作。

读取操作：

* EEPROM存储器的I2C地址
* EEPROM内部地址（存储数据的地址）
* 读取数值

写入操作：

* EEPROM存储器的I2C地址
* EEPROM内部地址（存储数据的地址）
* 写入数值

在BiBoard的例程中，我们的EEPROM在I2C总线上的地址是0x54，容量为8192Bytes（64Kbit）。我们往EEPROM里从第一个地址开始顺序写入0到15一共16个数值，然后再读出来进行对比。理论上EEPROM写入的数值和对应的地址应该相同。

在NyBoard出厂测试中，我们也是使用这种方法，只不过更复杂一些。我们会使用固定列表填满EEPROM再读取出来进行对比。

```
#include <Wire.h>

#define EEPROM_ADDRESS 0x54
#define EEPROM_CAPACITY 8192       // 64Kbit
#define EEPROM_TESTBYTES 16

// write 1 byte EEPROM by address
void writeEEPROM(int deviceaddress, unsigned int eeaddress, byte data ) 
{
  Wire.beginTransmission(deviceaddress);
  Wire.write((int)(eeaddress >> 8));   // MSB
  Wire.write((int)(eeaddress & 0xFF)); // LSB
  Wire.write(data);
  Wire.endTransmission();
 
  delay(5);
}

// read 1 byte EEPROM by address
byte readEEPROM(int deviceaddress, unsigned int eeaddress ) 
{
  byte rdata = 0xFF;
 
  Wire.beginTransmission(deviceaddress);
  Wire.write((int)(eeaddress >> 8));   // MSB
  Wire.write((int)(eeaddress & 0xFF)); // LSB
  Wire.endTransmission();
 
  Wire.requestFrom(deviceaddress,1);
 
  if (Wire.available()) 
    rdata = Wire.read();
  return rdata;
}

void testI2CEEPROM(){

    byte tmpData = 0;

    Serial.println("EEPROM Testing...");
    
    // write EEPROM from 0 to EEPROM_TESTBYTES
    for(int i = 0; i < EEPROM_TESTBYTES; i++){
        writeEEPROM(EEPROM_ADDRESS, i, i % 256);
        delay(1);
    }

    Serial.println();
    
    // read from 0 to EEPROM_TESTBYTES
    for(int i = 0; i < EEPROM_TESTBYTES; i++){
        tmpData =  (int)readEEPROM(EEPROM_ADDRESS, i);
        Serial.print(tmpData);
        Serial.print("\t");
    }
}


void setup(){

    Serial.begin(115200);
    Wire.begin();
    
    testI2CEEPROM();
}

void loop(){
  
}
```

最后一点需要注意，EEPROM的操作，尤其是写入操作一般不会放入loop()循环当中。虽然EEPROM很耐擦写（10万次），但如果在loop循环中频繁写入某一个块，会导致EEPROM出故障的。


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