
#include "clI2CScanner.h"

#include <Adafruit_SSD1306.h>
#include <Adafruit_GFX.h>
#define OLED_RESET -1 // Reset pin # (or -1 if sharing Arduino reset pin)
#define SCREEN_WIDTH 128 // OLED Display Breite, in pixels
#define SCREEN_HEIGHT 64 // OLED Display Höhe, in pixels
Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire,OLED_RESET);

clI2CScanner SCANNER;

void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);
  Serial.println("I2C-Scanner ESP32");
  SCANNER.ZeigeVorhandeneI2CGeraete();
  SCANNER.IstI2CGeraetDa(0x28);
  Serial.println(SCANNER.GetI2CStatusMeldung());
  display.begin(SSD1306_SWITCHCAPVCC, 0x3C);
  delay(1000);
  display.clearDisplay();
  display.setTextSize(1);
  display.setTextColor(WHITE);
  display.setCursor(0, 0);
  display.print("012345678901234567890");

  display.setCursor(0, 8);
  display.print("012345678901234567890");

  display.setCursor(0, 16);
  display.print("012345678901234567890");

  display.setCursor(0, 24);
  display.print("012345678901234567890");

  display.setCursor(0, 32);
  display.print("012345678901234567890");

 display.setCursor(0, 40);
  display.print("012345678901234567890");

 display.setCursor(0, 48);
  display.print("012345678901234567890");

   display.setCursor(0, 56);
  display.print("012345678901234567890");


  //display.setTextColor(BLACK, WHITE);
  display.display();
  display.startscrollright(0x02, 0x03);
}

void loop() {
 
  // put your main code here, to run repeatedly:
  delay(1000); // this speeds up the simulation
}


I2CScanner.ino

diagram.json

/*
#################################################################################################################################
                                                       clI2CScanner.h
                                     (c) Walther Gugeler Mail: walther.gugeler@gmail.com

                                                    Version : 07.12.2022
#################################################################################################################################
*/                                                    
#ifndef clI2CScanner20221207_h
#define clI2CScanner20221207_h
#include <Arduino.h>
#include <vector>
class clI2CScanner
{
  public:
  clI2CScanner();
  bool IstI2CGeraetDa(byte bSensorAdr);
  void ZeigeVorhandeneI2CGeraete ();
  String GetI2CStatusMeldung();
  private:
  struct _struSensorBezeichnungen
  {byte bSensorAdr;String strSensorname;} ;
  typedef struct _struSensorBezeichnungen _SENSORBEZ;
  std::vector <_SENSORBEZ> _veSensorBezeichnungen;
  String _strStatusMeldung="";
  void _SetBezeichner(byte bSensorAdr,String strSensorname);
  void _InitBezeichner();
  String _GetBezeichner(byte bSensorAdr);
  void _SetStatusMeldung (byte bSensorAdr,byte bError);
};

#endif /* clI2CScanner20221207_h */


clI2CScanner.h

/*
#################################################################################################################################
                                                       clI2CScanner.cpp
                                     (c) Walther Gugeler Mail: walther.gugeler@gmail.com

                                                    Version : 07.12.2022
#################################################################################################################################
*/   
#include "clI2CScanner.h"
#include <Wire.h>
#define PIN_DA 21
#define PIN_CL 22
//---------------------------------------------------------------------------------------------------------------------------------
//                                                                                                       Konstruktor clI2CScanner()
//---------------------------------------------------------------------------------------------------------------------------------
clI2CScanner:: clI2CScanner() 
  {Wire.begin(PIN_DA,PIN_CL); this->_InitBezeichner();this->_strStatusMeldung="";} 
//---------------------------------------------------------------------------------------------------------------------------------
//                                                          void clI2CScanner::_SetBezeichner(byte bSensorAdr,String strSensorname)
//---------------------------------------------------------------------------------------------------------------------------------
void clI2CScanner::_SetBezeichner(byte bSensorAdr,String strSensorname)
{
  _SENSORBEZ _AktBez;
  _AktBez.bSensorAdr = bSensorAdr; _AktBez.strSensorname =strSensorname;
  this->_veSensorBezeichnungen.push_back(_AktBez);
}
//---------------------------------------------------------------------------------------------------------------------------------
//                                                                                             void clI2CScanner::_InitBezeichner()
// Initialisierung der bekannten I2C-Adressen mit den daran angeschlossenen Geräten
//---------------------------------------------------------------------------------------------------------------------------------
void clI2CScanner::_InitBezeichner()
{
  this->_SetBezeichner(39,"LCD-Display");
  this->_SetBezeichner(104,"RTC-Uhr");
  this->_SetBezeichner(87,"RTC-Uhr EPROM");
}
//---------------------------------------------------------------------------------------------------------------------------------
//                                                                            String clI2CScanner::_GetBezeichner(byte bSensorAdr)
//---------------------------------------------------------------------------------------------------------------------------------
String clI2CScanner::_GetBezeichner(byte bSensorAdr)
{
  String _Info="";
  for (int i=0; i <  this->_veSensorBezeichnungen.size();i++)
  {
    if ( this->_veSensorBezeichnungen[i].bSensorAdr == bSensorAdr)
    {
      _Info+="I2C-Adresse Hex: "; _Info+=String(bSensorAdr,HEX);
      _Info+=" Dez: ";  _Info+=String(bSensorAdr,DEC);
      if (bSensorAdr < 100) _Info+=" "; if (bSensorAdr < 10) _Info+=" ";
      _Info+=" Geraet : "; _Info+=this->_veSensorBezeichnungen[i].strSensorname;
      return(_Info);
    }
  }
  _Info+="I2C-Adresse Hex: "; _Info+=String(bSensorAdr,HEX);
  _Info+=" Dez: ";  _Info+=String(bSensorAdr,DEC);
  if (bSensorAdr < 100) _Info+=" "; if (bSensorAdr < 10) _Info+=" ";
  _Info+=" Geraetebezeichnung unbekannt ";   
  return (_Info);
}
//---------------------------------------------------------------------------------------------------------------------------------
//                                                                               bool clI2CScanner::IstI2CGeraetDa(byte bSensorAdr)
//---------------------------------------------------------------------------------------------------------------------------------
bool clI2CScanner::IstI2CGeraetDa(byte bSensorAdr)
{
  byte bError;
  Wire.beginTransmission(bSensorAdr); bError = Wire.endTransmission();
  this->_SetStatusMeldung (bSensorAdr,bError);
  if (bError == 0) return (true);
  return (false);
}
//---------------------------------------------------------------------------------------------------------------------------------
//                                                                                  void clI2CScanner::ZeigeVorhandeneI2CGeraete ()
//---------------------------------------------------------------------------------------------------------------------------------
void clI2CScanner::ZeigeVorhandeneI2CGeraete ()
{
  byte error,addresse;
  for (addresse=1; addresse < 127; addresse++)
  {
    if (this->IstI2CGeraetDa(addresse)) {Serial.println(this->_GetBezeichner(addresse));}
  }  
}
//---------------------------------------------------------------------------------------------------------------------------------
//                                                              void clI2CScanner::_SetStatusMeldung ((byte bSensorAdr,byte bError)
//---------------------------------------------------------------------------------------------------------------------------------
void clI2CScanner::_SetStatusMeldung (byte bSensorAdr,byte bError)
{
  this->_strStatusMeldung="";
  this->_strStatusMeldung+="I2C-Adresse Hex: "; this->_strStatusMeldung+=String(bSensorAdr,HEX);
  this->_strStatusMeldung+=" Dez: ";  this->_strStatusMeldung+=String(bSensorAdr,DEC); 
  if (bSensorAdr < 100)  this->_strStatusMeldung+=" "; if (bSensorAdr < 10)  this->_strStatusMeldung+=" ";
  switch (bError)
  {
     case 0 :  this->_strStatusMeldung = this->_GetBezeichner(bSensorAdr); break;
     case 1 :  this->_strStatusMeldung+=" Datenblock an I2C-Geraet zu gross"; break;
     case 2 :  this->_strStatusMeldung+=" Kein I2C-Geraet gefunden"; break;
     case 3 :  this->_strStatusMeldung+=" Fehler bei Daten an I2C-Geraet aufgetreten"; break;
     case 4 :  this->_strStatusMeldung+=" Unbekanter Fehler bei I2C-Uebtragung"; break;
     default:  this->_strStatusMeldung+=" Unbekanter Fehlercode bei I2C-Uebtragung"; break;             
  }
}
//---------------------------------------------------------------------------------------------------------------------------------
//                                                                                        String clI2CScanner::GetI2CStatusMeldung()
//---------------------------------------------------------------------------------------------------------------------------------
String clI2CScanner::GetI2CStatusMeldung(){return (this->_strStatusMeldung);}

clI2CScanner.cpp

# Wokwi Library List
# See https://docs.wokwi.com/guides/libraries

LiquidCrystal I2C
Adafruit SSD1306
Adafruit GFX Library

libraries.txt

// Code by JeeLabs http://news.jeelabs.org/code/
// Released to the public domain! Enjoy!

#include <Wire.h>
#include "clRtcLib.h"
#ifdef __AVR__
 #include <avr/pgmspace.h>
#elif defined(ESP8266)
 #include <pgmspace.h>
#elif defined(ARDUINO_ARCH_SAMD)
// nothing special needed
#elif defined(ARDUINO_SAM_DUE)
 #define PROGMEM
 #define pgm_read_byte(addr) (*(const unsigned char *)(addr))
 #define Wire Wire1
#endif



#if (ARDUINO >= 100)
 #include <Arduino.h> // capital A so it is error prone on case-sensitive filesystems
 // Macro to deal with the difference in I2C write functions from old and new Arduino versions.
 #define _I2C_WRITE write
 #define _I2C_READ  read
#else
 #include <WProgram.h>
 #define _I2C_WRITE send
 #define _I2C_READ  receive
#endif


static uint8_t read_i2c_register(uint8_t addr, uint8_t reg) {
  Wire.beginTransmission(addr);
  Wire._I2C_WRITE((byte)reg);
  Wire.endTransmission();

  Wire.requestFrom(addr, (byte)1);
  return Wire._I2C_READ();
}

static void write_i2c_register(uint8_t addr, uint8_t reg, uint8_t val) {
  Wire.beginTransmission(addr);
  Wire._I2C_WRITE((byte)reg);
  Wire._I2C_WRITE((byte)val);
  Wire.endTransmission();
}


////////////////////////////////////////////////////////////////////////////////
// utility code, some of this could be exposed in the DateTime API if needed

const uint8_t daysInMonth [] PROGMEM = { 31,28,31,30,31,30,31,31,30,31,30,31 };

// number of days since 2000/01/01, valid for 2001..2099
static uint16_t date2days(uint16_t y, uint8_t m, uint8_t d) {
    if (y >= 2000)
        y -= 2000;
    uint16_t days = d;
    for (uint8_t i = 1; i < m; ++i)
        days += pgm_read_byte(daysInMonth + i - 1);
    if (m > 2 && y % 4 == 0)
        ++days;
    return days + 365 * y + (y + 3) / 4 - 1;
}

static long time2long(uint16_t days, uint8_t h, uint8_t m, uint8_t s) {
    return ((days * 24L + h) * 60 + m) * 60 + s;
}

////////////////////////////////////////////////////////////////////////////////
// DateTime implementation - ignores time zones and DST changes
// NOTE: also ignores leap seconds, see http://en.wikipedia.org/wiki/Leap_second

DateTime::DateTime (uint32_t t) {
  t -= SECONDS_FROM_1970_TO_2000;    // bring to 2000 timestamp from 1970

    ss = t % 60;
    t /= 60;
    mm = t % 60;
    t /= 60;
    hh = t % 24;
    uint16_t days = t / 24;
    uint8_t leap;
    for (yOff = 0; ; ++yOff) {
        leap = yOff % 4 == 0;
        if (days < 365 + leap)
            break;
        days -= 365 + leap;
    }
    for (m = 1; ; ++m) {
        uint8_t daysPerMonth = pgm_read_byte(daysInMonth + m - 1);
        if (leap && m == 2)
            ++daysPerMonth;
        if (days < daysPerMonth)
            break;
        days -= daysPerMonth;
    }
    d = days + 1;
}

DateTime::DateTime (uint16_t year, uint8_t month, uint8_t day, uint8_t hour, uint8_t min, uint8_t sec) {
    if (year >= 2000)
        year -= 2000;
    yOff = year;
    m = month;
    d = day;
    hh = hour;
    mm = min;
    ss = sec;
}

DateTime::DateTime (const DateTime& copy):
  yOff(copy.yOff),
  m(copy.m),
  d(copy.d),
  hh(copy.hh),
  mm(copy.mm),
  ss(copy.ss)
{}

static uint8_t conv2d(const char* p) {
    uint8_t v = 0;
    if ('0' <= *p && *p <= '9')
        v = *p - '0';
    return 10 * v + *++p - '0';
}

// A convenient constructor for using "the compiler's time":
//   DateTime now (__DATE__, __TIME__);
// NOTE: using F() would further reduce the RAM footprint, see below.
DateTime::DateTime (const char* date, const char* time) {
    // sample input: date = "Dec 26 2009", time = "12:34:56"
    yOff = conv2d(date + 9);
    // Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 
    switch (date[0]) {
        case 'J': m = (date[1] == 'a') ? 1 : ((date[2] == 'n') ? 6 : 7); break;
        case 'F': m = 2; break;
        case 'A': m = date[2] == 'r' ? 4 : 8; break;
        case 'M': m = date[2] == 'r' ? 3 : 5; break;
        case 'S': m = 9; break;
        case 'O': m = 10; break;
        case 'N': m = 11; break;
        case 'D': m = 12; break;
    }
    d = conv2d(date + 4);
    hh = conv2d(time);
    mm = conv2d(time + 3);
    ss = conv2d(time + 6);
}

// A convenient constructor for using "the compiler's time":
// This version will save RAM by using PROGMEM to store it by using the F macro.
//   DateTime now (F(__DATE__), F(__TIME__));
DateTime::DateTime (const __FlashStringHelper* date, const __FlashStringHelper* time) {
    // sample input: date = "Dec 26 2009", time = "12:34:56"
    char buff[11];
    memcpy_P(buff, date, 11);
    yOff = conv2d(buff + 9);
    // Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    switch (buff[0]) {
        case 'J': m = (buff[1] == 'a') ? 1 : ((buff[2] == 'n') ? 6 : 7); break;
        case 'F': m = 2; break;
        case 'A': m = buff[2] == 'r' ? 4 : 8; break;
        case 'M': m = buff[2] == 'r' ? 3 : 5; break;
        case 'S': m = 9; break;
        case 'O': m = 10; break;
        case 'N': m = 11; break;
        case 'D': m = 12; break;
    }
    d = conv2d(buff + 4);
    memcpy_P(buff, time, 8);
    hh = conv2d(buff);
    mm = conv2d(buff + 3);
    ss = conv2d(buff + 6);
}

uint8_t DateTime::dayOfTheWeek() const {    
    uint16_t day = date2days(yOff, m, d);
    return (day + 6) % 7; // Jan 1, 2000 is a Saturday, i.e. returns 6
}

uint32_t DateTime::unixtime(void) const {
  uint32_t t;
  uint16_t days = date2days(yOff, m, d);
  t = time2long(days, hh, mm, ss);
  t += SECONDS_FROM_1970_TO_2000;  // seconds from 1970 to 2000

  return t;
}

long DateTime::secondstime(void) const {
  long t;
  uint16_t days = date2days(yOff, m, d);
  t = time2long(days, hh, mm, ss);
  return t;
}

DateTime DateTime::operator+(const TimeSpan& span) {
  return DateTime(unixtime()+span.totalseconds());
}

DateTime DateTime::operator-(const TimeSpan& span) {
  return DateTime(unixtime()-span.totalseconds());
}

TimeSpan DateTime::operator-(const DateTime& right) {
  return TimeSpan(unixtime()-right.unixtime());
}

////////////////////////////////////////////////////////////////////////////////
// TimeSpan implementation

TimeSpan::TimeSpan (int32_t seconds):
  _seconds(seconds)
{}

TimeSpan::TimeSpan (int16_t days, int8_t hours, int8_t minutes, int8_t seconds):
  _seconds((int32_t)days*86400L + (int32_t)hours*3600 + (int32_t)minutes*60 + seconds)
{}

TimeSpan::TimeSpan (const TimeSpan& copy):
  _seconds(copy._seconds)
{}

TimeSpan TimeSpan::operator+(const TimeSpan& right) {
  return TimeSpan(_seconds+right._seconds);
}

TimeSpan TimeSpan::operator-(const TimeSpan& right) {
  return TimeSpan(_seconds-right._seconds);
}

////////////////////////////////////////////////////////////////////////////////
// RTC_DS1307 implementation

static uint8_t bcd2bin (uint8_t val) { return val - 6 * (val >> 4); }
static uint8_t bin2bcd (uint8_t val) { return val + 6 * (val / 10); }

boolean RTC_DS1307::begin(void) {
  Wire.begin();
  return true;
}

uint8_t RTC_DS1307::isrunning(void) {
  Wire.beginTransmission(DS1307_ADDRESS);
  Wire._I2C_WRITE((byte)0);
  Wire.endTransmission();

  Wire.requestFrom(DS1307_ADDRESS, 1);
  uint8_t ss = Wire._I2C_READ();
  return !(ss>>7);
}

void RTC_DS1307::adjust(const DateTime& dt) {
  Wire.beginTransmission(DS1307_ADDRESS);
  Wire._I2C_WRITE((byte)0); // start at location 0
  Wire._I2C_WRITE(bin2bcd(dt.second()));
  Wire._I2C_WRITE(bin2bcd(dt.minute()));
  Wire._I2C_WRITE(bin2bcd(dt.hour()));
  Wire._I2C_WRITE(bin2bcd(0));
  Wire._I2C_WRITE(bin2bcd(dt.day()));
  Wire._I2C_WRITE(bin2bcd(dt.month()));
  Wire._I2C_WRITE(bin2bcd(dt.year() - 2000));
  Wire.endTransmission();
}

DateTime RTC_DS1307::now() {
  Wire.beginTransmission(DS1307_ADDRESS);
  Wire._I2C_WRITE((byte)0);	
  Wire.endTransmission();

  Wire.requestFrom(DS1307_ADDRESS, 7);
  uint8_t ss = bcd2bin(Wire._I2C_READ() & 0x7F);
  uint8_t mm = bcd2bin(Wire._I2C_READ());
  uint8_t hh = bcd2bin(Wire._I2C_READ());
  Wire._I2C_READ();
  uint8_t d = bcd2bin(Wire._I2C_READ());
  uint8_t m = bcd2bin(Wire._I2C_READ());
  uint16_t y = bcd2bin(Wire._I2C_READ()) + 2000;
  
  return DateTime (y, m, d, hh, mm, ss);
}

Ds1307SqwPinMode RTC_DS1307::readSqwPinMode() {
  int mode;

  Wire.beginTransmission(DS1307_ADDRESS);
  Wire._I2C_WRITE(DS1307_CONTROL);
  Wire.endTransmission();
  
  Wire.requestFrom((uint8_t)DS1307_ADDRESS, (uint8_t)1);
  mode = Wire._I2C_READ();

  mode &= 0x93;
  return static_cast<Ds1307SqwPinMode>(mode);
}

void RTC_DS1307::writeSqwPinMode(Ds1307SqwPinMode mode) {
  Wire.beginTransmission(DS1307_ADDRESS);
  Wire._I2C_WRITE(DS1307_CONTROL);
  Wire._I2C_WRITE(mode);
  Wire.endTransmission();
}

void RTC_DS1307::readnvram(uint8_t* buf, uint8_t size, uint8_t address) {
  int addrByte = DS1307_NVRAM + address;
  Wire.beginTransmission(DS1307_ADDRESS);
  Wire._I2C_WRITE(addrByte);
  Wire.endTransmission();
  
  Wire.requestFrom((uint8_t) DS1307_ADDRESS, size);
  for (uint8_t pos = 0; pos < size; ++pos) {
    buf[pos] = Wire._I2C_READ();
  }
}

void RTC_DS1307::writenvram(uint8_t address, uint8_t* buf, uint8_t size) {
  int addrByte = DS1307_NVRAM + address;
  Wire.beginTransmission(DS1307_ADDRESS);
  Wire._I2C_WRITE(addrByte);
  for (uint8_t pos = 0; pos < size; ++pos) {
    Wire._I2C_WRITE(buf[pos]);
  }
  Wire.endTransmission();
}

uint8_t RTC_DS1307::readnvram(uint8_t address) {
  uint8_t data;
  readnvram(&data, 1, address);
  return data;
}

void RTC_DS1307::writenvram(uint8_t address, uint8_t data) {
  writenvram(address, &data, 1);
}

////////////////////////////////////////////////////////////////////////////////
// RTC_Millis implementation

long RTC_Millis::offset = 0;

void RTC_Millis::adjust(const DateTime& dt) {
    offset = dt.unixtime() - millis() / 1000;
}

DateTime RTC_Millis::now() {
  return (uint32_t)(offset + millis() / 1000);
}

////////////////////////////////////////////////////////////////////////////////

////////////////////////////////////////////////////////////////////////////////
// RTC_PCF8563 implementation

boolean RTC_PCF8523::begin(void) {
  Wire.begin();
  return true;
}

boolean RTC_PCF8523::initialized(void) {
  Wire.beginTransmission(PCF8523_ADDRESS);
  Wire._I2C_WRITE((byte)PCF8523_CONTROL_3);
  Wire.endTransmission();

  Wire.requestFrom(PCF8523_ADDRESS, 1);
  uint8_t ss = Wire._I2C_READ();
  return ((ss & 0xE0) != 0xE0);
}

void RTC_PCF8523::adjust(const DateTime& dt) {
  Wire.beginTransmission(PCF8523_ADDRESS);
  Wire._I2C_WRITE((byte)3); // start at location 3
  Wire._I2C_WRITE(bin2bcd(dt.second()));
  Wire._I2C_WRITE(bin2bcd(dt.minute()));
  Wire._I2C_WRITE(bin2bcd(dt.hour()));
  Wire._I2C_WRITE(bin2bcd(dt.day()));
  Wire._I2C_WRITE(bin2bcd(0)); // skip weekdays
  Wire._I2C_WRITE(bin2bcd(dt.month()));
  Wire._I2C_WRITE(bin2bcd(dt.year() - 2000));
  Wire.endTransmission();

  // set to battery switchover mode
  Wire.beginTransmission(PCF8523_ADDRESS);
  Wire._I2C_WRITE((byte)PCF8523_CONTROL_3);
  Wire._I2C_WRITE((byte)0x00);
  Wire.endTransmission();
}

DateTime RTC_PCF8523::now() {
  Wire.beginTransmission(PCF8523_ADDRESS);
  Wire._I2C_WRITE((byte)3);	
  Wire.endTransmission();

  Wire.requestFrom(PCF8523_ADDRESS, 7);
  uint8_t ss = bcd2bin(Wire._I2C_READ() & 0x7F);
  uint8_t mm = bcd2bin(Wire._I2C_READ());
  uint8_t hh = bcd2bin(Wire._I2C_READ());
  uint8_t d = bcd2bin(Wire._I2C_READ());
  Wire._I2C_READ();  // skip 'weekdays'
  uint8_t m = bcd2bin(Wire._I2C_READ());
  uint16_t y = bcd2bin(Wire._I2C_READ()) + 2000;
  
  return DateTime (y, m, d, hh, mm, ss);
}

Pcf8523SqwPinMode RTC_PCF8523::readSqwPinMode() {
  int mode;

  Wire.beginTransmission(PCF8523_ADDRESS);
  Wire._I2C_WRITE(PCF8523_CLKOUTCONTROL);
  Wire.endTransmission();
  
  Wire.requestFrom((uint8_t)PCF8523_ADDRESS, (uint8_t)1);
  mode = Wire._I2C_READ();

  mode >>= 3;
  mode &= 0x7;
  return static_cast<Pcf8523SqwPinMode>(mode);
}

void RTC_PCF8523::writeSqwPinMode(Pcf8523SqwPinMode mode) {
  Wire.beginTransmission(PCF8523_ADDRESS);
  Wire._I2C_WRITE(PCF8523_CLKOUTCONTROL);
  Wire._I2C_WRITE(mode << 3);
  Wire.endTransmission();
}




////////////////////////////////////////////////////////////////////////////////
// RTC_DS3231 implementation

boolean RTC_DS3231::begin(void) {
  Wire.begin();
  return true;
}

bool RTC_DS3231::lostPower(void) {
  return (read_i2c_register(DS3231_ADDRESS, DS3231_STATUSREG) >> 7);
}

void RTC_DS3231::adjust(const DateTime& dt) {
  Wire.beginTransmission(DS3231_ADDRESS);
  Wire._I2C_WRITE((byte)0); // start at location 0
  Wire._I2C_WRITE(bin2bcd(dt.second()));
  Wire._I2C_WRITE(bin2bcd(dt.minute()));
  Wire._I2C_WRITE(bin2bcd(dt.hour()));
  Wire._I2C_WRITE(bin2bcd(0));
  Wire._I2C_WRITE(bin2bcd(dt.day()));
  Wire._I2C_WRITE(bin2bcd(dt.month()));
  Wire._I2C_WRITE(bin2bcd(dt.year() - 2000));
  Wire.endTransmission();

  uint8_t statreg = read_i2c_register(DS3231_ADDRESS, DS3231_STATUSREG);
  statreg &= ~0x80; // flip OSF bit
  write_i2c_register(DS3231_ADDRESS, DS3231_STATUSREG, statreg);
}

DateTime RTC_DS3231::now() {
  Wire.beginTransmission(DS3231_ADDRESS);
  Wire._I2C_WRITE((byte)0);	
  Wire.endTransmission();

  Wire.requestFrom(DS3231_ADDRESS, 7);
  uint8_t ss = bcd2bin(Wire._I2C_READ() & 0x7F);
  uint8_t mm = bcd2bin(Wire._I2C_READ());
  uint8_t hh = bcd2bin(Wire._I2C_READ());
  Wire._I2C_READ();
  uint8_t d = bcd2bin(Wire._I2C_READ());
  uint8_t m = bcd2bin(Wire._I2C_READ());
  uint16_t y = bcd2bin(Wire._I2C_READ()) + 2000;
  
  return DateTime (y, m, d, hh, mm, ss);
}

Ds3231SqwPinMode RTC_DS3231::readSqwPinMode() {
  int mode;

  Wire.beginTransmission(DS3231_ADDRESS);
  Wire._I2C_WRITE(DS3231_CONTROL);
  Wire.endTransmission();
  
  Wire.requestFrom((uint8_t)DS3231_ADDRESS, (uint8_t)1);
  mode = Wire._I2C_READ();

  mode &= 0x93;
  return static_cast<Ds3231SqwPinMode>(mode);
}

void RTC_DS3231::writeSqwPinMode(Ds3231SqwPinMode mode) {
  uint8_t ctrl;
  ctrl = read_i2c_register(DS3231_ADDRESS, DS3231_CONTROL);

  ctrl &= ~0x04; // turn off INTCON
  ctrl &= ~0x18; // set freq bits to 0

  if (mode == DS3231_OFF) {
    ctrl |= 0x04; // turn on INTCN
  } else {
    ctrl |= mode;
  } 
  write_i2c_register(DS3231_ADDRESS, DS3231_CONTROL, ctrl);

  //Serial.println( read_i2c_register(DS3231_ADDRESS, DS3231_CONTROL), HEX);
}


clRtcLib.cpp

// Code by JeeLabs http://news.jeelabs.org/code/
// Released to the public domain! Enjoy!

#ifndef _RTCLIB_H_
#define _RTCLIB_H_

#include <Arduino.h>
class TimeSpan;


#define PCF8523_ADDRESS       0x68
#define PCF8523_CLKOUTCONTROL 0x0F
#define PCF8523_CONTROL_3     0x02

#define DS1307_ADDRESS  0x68
#define DS1307_CONTROL  0x07
#define DS1307_NVRAM    0x08

#define DS3231_ADDRESS  0x68
#define DS3231_CONTROL  0x0E
#define DS3231_STATUSREG 0x0F

#define SECONDS_PER_DAY 86400L

#define SECONDS_FROM_1970_TO_2000 946684800



// Simple general-purpose date/time class (no TZ / DST / leap second handling!)
class DateTime {
public:
    DateTime (uint32_t t =0);
    DateTime (uint16_t year, uint8_t month, uint8_t day,
                uint8_t hour =0, uint8_t min =0, uint8_t sec =0);
    DateTime (const DateTime& copy);
    DateTime (const char* date, const char* time);
    DateTime (const __FlashStringHelper* date, const __FlashStringHelper* time);
    uint16_t year() const       { return 2000 + yOff; }
    uint8_t month() const       { return m; }
    uint8_t day() const         { return d; }
    uint8_t hour() const        { return hh; }
    uint8_t minute() const      { return mm; }
    uint8_t second() const      { return ss; }
    uint8_t dayOfTheWeek() const;

    // 32-bit times as seconds since 1/1/2000
    long secondstime() const;   
    // 32-bit times as seconds since 1/1/1970
    uint32_t unixtime(void) const;

    DateTime operator+(const TimeSpan& span);
    DateTime operator-(const TimeSpan& span);
    TimeSpan operator-(const DateTime& right);

protected:
    uint8_t yOff, m, d, hh, mm, ss;
};

// Timespan which can represent changes in time with seconds accuracy.
class TimeSpan {
public:
    TimeSpan (int32_t seconds = 0);
    TimeSpan (int16_t days, int8_t hours, int8_t minutes, int8_t seconds);
    TimeSpan (const TimeSpan& copy);
    int16_t days() const         { return _seconds / 86400L; }
    int8_t  hours() const        { return _seconds / 3600 % 24; }
    int8_t  minutes() const      { return _seconds / 60 % 60; }
    int8_t  seconds() const      { return _seconds % 60; }
    int32_t totalseconds() const { return _seconds; }

    TimeSpan operator+(const TimeSpan& right);
    TimeSpan operator-(const TimeSpan& right);

protected:
    int32_t _seconds;
};

// RTC based on the DS1307 chip connected via I2C and the Wire library
enum Ds1307SqwPinMode { OFF = 0x00, ON = 0x80, SquareWave1HZ = 0x10, SquareWave4kHz = 0x11, SquareWave8kHz = 0x12, SquareWave32kHz = 0x13 };

class RTC_DS1307 {
public:
    boolean begin(void);
    static void adjust(const DateTime& dt);
    uint8_t isrunning(void);
    static DateTime now();
    static Ds1307SqwPinMode readSqwPinMode();
    static void writeSqwPinMode(Ds1307SqwPinMode mode);
    uint8_t readnvram(uint8_t address);
    void readnvram(uint8_t* buf, uint8_t size, uint8_t address);
    void writenvram(uint8_t address, uint8_t data);
    void writenvram(uint8_t address, uint8_t* buf, uint8_t size);
};

// RTC based on the DS3231 chip connected via I2C and the Wire library
enum Ds3231SqwPinMode { DS3231_OFF = 0x01, DS3231_SquareWave1Hz = 0x00, DS3231_SquareWave1kHz = 0x08, DS3231_SquareWave4kHz = 0x10, DS3231_SquareWave8kHz = 0x18 };

class RTC_DS3231 {
public:
    boolean begin(void);
    static void adjust(const DateTime& dt);
    bool lostPower(void);
    static DateTime now();
    static Ds3231SqwPinMode readSqwPinMode();
    static void writeSqwPinMode(Ds3231SqwPinMode mode);
};


// RTC based on the PCF8523 chip connected via I2C and the Wire library
enum Pcf8523SqwPinMode { PCF8523_OFF = 7, PCF8523_SquareWave1HZ = 6, PCF8523_SquareWave32HZ = 5, PCF8523_SquareWave1kHz = 4, PCF8523_SquareWave4kHz = 3, PCF8523_SquareWave8kHz = 2, PCF8523_SquareWave16kHz = 1, PCF8523_SquareWave32kHz = 0 };

class RTC_PCF8523 {
public:
    boolean begin(void);
    void adjust(const DateTime& dt);
    boolean initialized(void);
    static DateTime now();

    Pcf8523SqwPinMode readSqwPinMode();
    void writeSqwPinMode(Pcf8523SqwPinMode mode);
};

// RTC using the internal millis() clock, has to be initialized before use
// NOTE: this clock won't be correct once the millis() timer rolls over (>49d?)
class RTC_Millis {
public:
    static void begin(const DateTime& dt) { adjust(dt); }
    static void adjust(const DateTime& dt);
    static DateTime now();

protected:
    static long offset;
};

#endif // _RTCLIB_H_
