Example of DS1307RTC Read&Write

RTC-ReadWrite.js

var five = new require('johnny-five');
var RTC = 0x68;
var board = new five.Board();
board.on("ready", function() {
    board.io.sendI2CConfig(0);
    setTime();
    setInterval(getTime,1000);
});

function fromBcd(num){
    return parseInt((num >> 4 & 0xf).toString() + (num & 0xf).toString());
}

function toBcd(num){
    return parseInt(num / 10) << 4 | parseInt(num % 10);
}

function pad(num){
    return ("0" + num).slice(-2);
}

function getTime(){
    //読み込みを始めるアドレスを書き込む
    board.io.sendI2CWriteRequest(RTC,[0x00]);
    board.io.sendI2CReadRequest(RTC,8,function(d){
        var year = 2000 + fromBcd(d[6]);
        var month = fromBcd(d[5]);
        var date = fromBcd(d[4]);
        var weekday = fromBcd(d[3]);//日曜日(1) - 土曜日(7)
        var hours = fromBcd(d[2]);
        var minutes = pad(fromBcd(d[1]));
        var seconds = pad(fromBcd(d[0]));
        console.log(year + "/" + month + "/" + date + " " + hours + ":" + minutes + ":" + seconds);
    });
}

function setTime(){
    var d = new Date();
    /*
    書き込むデータを配列で用意する
    書き込み開始アドレス、秒、分、時、曜日、日、月、年の順番
    曜日は1が日曜日なので＋１
    月は１が１月なので＋１
    年は二桁なので－１００
    */
    var dates = [
        0x00
        ,toBcd(d.getSeconds())
        ,toBcd(d.getMinutes())
        ,toBcd(d.getHours())
        ,toBcd(d.getDay() + 1)
        ,toBcd(d.getDate())
        ,toBcd(d.getMonth() + 1)
        ,toBcd(d.getYear() - 100)
    ];
    board.io.sendI2CWriteRequest(RTC,dates);
}