//define bidirectional address-data bus
#define ad0 2
#define ad1 3
#define ad2 4
#define ad3 5
#define ad4 6
#define ad5 7
#define ad6 8
#define ad7 9
//ALE or address strobe (AS pin)
#define as 10
//RD or OE (DS pin )
#define ds 12
//WR or (RW pin)
#define rw 11

#define regA 0x0A
#define regB 0x0B
//RO registers C,D
#define regC 0x0C
#define regD 0x0D

void bus2out();
void bus2in();

byte readbyte(byte address);
void writebyte(byte address,byte value);
boolean adjust(byte address);

char msgs[7][4] = {"Sun","Mon", "Tue", "Wed", "Thu", "Fri", "Sat"};

void setup()
{
  Serial.begin(9600);
  pinMode(as, OUTPUT);
  pinMode(ds, OUTPUT);
  pinMode(rw, OUTPUT);
  //delay after power up to start-up
  digitalWrite(as,LOW);
  digitalWrite(ds,LOW);
  digitalWrite(rw,LOW);
  delay(200);//to finish power set up
}


void loop()
{
 
  if (Serial.available() > 0) {
     int inByte = Serial.read();
 
     switch (inByte) {
     case 'h': 
          if (adjust(4)) Serial.println("Hours updated"); 
       break;
     case 'm':    
          if (adjust(2)) Serial.println("Minutes updated"); 
       break;
     case 'D':    
          if (adjust(7)) Serial.println("Day updated"); 
       break;
     case 'M':    
          if (adjust(8)) Serial.println("Month updated"); 
       break;
     case 'Y':    
          if (adjust(9)) Serial.println("Year updated"); 
       break;
     case 's':    
          if (adjust(0)) Serial.println("Seconds reset"); 
       break;
     case 't':    
       //show current time and date
        //test UIP (update in progress) bit in Reg A
        if (!bitRead(readbyte(regA),7))
          {
          Serial.print(readbyte(4),DEC); 
          Serial.print(':'); 
          Serial.print(readbyte(2),DEC);  
          Serial.print(':'); 
          Serial.print(readbyte(0),DEC); 
          Serial.print(' ');
          Serial.print(readbyte(7),DEC); 
          Serial.print('.'); 
          Serial.print(readbyte(8),DEC);  
          Serial.print('.'); 
          Serial.print(readbyte(9),DEC);      
          Serial.print(' ');
          byte day = readbyte(6)-1; // 1=Sunday
          char* msg = msgs[day];
          Serial.print(msg);
          Serial.println();   
          }
       break;
     case 'R':    
       //show regs values
          Serial.print("A: ");
          Serial.print(readbyte(regA),BIN);
          Serial.println();
          Serial.print("B: ");
          Serial.print(readbyte(regB),BIN);
          Serial.println();
          Serial.print("C: ");
          Serial.print(readbyte(regC),BIN);
          Serial.println();
          Serial.print("D: ");
          Serial.print(readbyte(regD),BIN);
          Serial.println();
       break;

     case 'i':
       //initalize
        byte b = readbyte(regB);
        b = b|0x80;
        writebyte(regB,b);
        b=b|0x07;
        writebyte(regB,b);
        
        writebyte(0,0x15);
        writebyte(1,0x15);
        writebyte(2,0x3A);
        writebyte(3,0x3A);
        writebyte(4,0x05);
        writebyte(5,0x05);
        writebyte(6,0x05);
        writebyte(7,0x03);
        writebyte(8,0x0C);
        writebyte(9,0x09);        

        b=b&0x7F;
        writebyte(regB,b);
        Serial.print("init done");
        Serial.println();
       break;       

//     default:

     } 
  }  
}//end of loop

void bus2out(){
  pinMode(ad0,OUTPUT);
  pinMode(ad1,OUTPUT);
  pinMode(ad2,OUTPUT);
  pinMode(ad3,OUTPUT);
  pinMode(ad4,OUTPUT);
  pinMode(ad5,OUTPUT);
  pinMode(ad6,OUTPUT);
  pinMode(ad7,OUTPUT);
}

void bus2in(){
  pinMode(ad0,INPUT);
  pinMode(ad1,INPUT);
  pinMode(ad2,INPUT);
  pinMode(ad3,INPUT);
  pinMode(ad4,INPUT);
  pinMode(ad5,INPUT);
  pinMode(ad6,INPUT);
  pinMode(ad7,INPUT);
}

byte readbyte(byte address){
  byte readb=0;
  
  //set address pins to output
  bus2out();
  //start READ cycle
  digitalWrite(rw,HIGH);
  //prepare to set address on bus
  digitalWrite(ds,HIGH);
  //delayMicroseconds(1);
  //set ALE high, on fall address latches
  digitalWrite(as,HIGH);
  //delayMicroseconds(1);
  //set address on bus 
  digitalWrite(ad0,bitRead(address,0));
  digitalWrite(ad1,bitRead(address,1));
  digitalWrite(ad2,bitRead(address,2));
  digitalWrite(ad3,bitRead(address,3));
  digitalWrite(ad4,bitRead(address,4));
  digitalWrite(ad5,bitRead(address,5));
  digitalWrite(ad6,bitRead(address,6));
  digitalWrite(ad7,bitRead(address,7));
  //delayMicroseconds(1);
  //set ALE low, latch address
  digitalWrite(as,LOW);
  bus2in();
  //delayMicroseconds(1);
  //finish address setting
  digitalWrite(ds,LOW);
  //wait for data from address
  //set bus for input
  //delayMicroseconds(1);
  //start reading data
  readb = digitalRead(ad0)|(digitalRead(ad1)<<1)|(digitalRead(ad2)<<2)|(digitalRead(ad3)<<3)|(digitalRead(ad4)<<4)|(digitalRead(ad5)<<5)|(digitalRead(ad6)<<6)|(digitalRead(ad7)<<7);
  digitalWrite(ds,HIGH);
  //delayMicroseconds(1);
  return readb;
}

void writebyte(byte address,byte value){

  //set address pins to output
  bus2out();
  //start READ cycle
  digitalWrite(rw,HIGH);
  //prepare to set address on bus
  digitalWrite(ds,HIGH);
  //delayMicroseconds(1);
  //set ALE high, on fall address latches
  digitalWrite(as,HIGH);
  //set address on bus 
  digitalWrite(ad0,bitRead(address,0));
  digitalWrite(ad1,bitRead(address,1));
  digitalWrite(ad2,bitRead(address,2));
  digitalWrite(ad3,bitRead(address,3));
  digitalWrite(ad4,bitRead(address,4));
  digitalWrite(ad5,bitRead(address,5));
  digitalWrite(ad6,bitRead(address,6));
  digitalWrite(ad7,bitRead(address,7));
  //set ALE low, latche address
  //delayMicroseconds(1);
  digitalWrite(as,LOW);
  //delayMicroseconds(1);
  digitalWrite(rw,LOW);
  //set byte to write
  digitalWrite(ad0,bitRead(value,0));
  digitalWrite(ad1,bitRead(value,1));
  digitalWrite(ad2,bitRead(value,2));
  digitalWrite(ad3,bitRead(value,3));
  digitalWrite(ad4,bitRead(value,4));
  digitalWrite(ad5,bitRead(value,5));
  digitalWrite(ad6,bitRead(value,6));
  digitalWrite(ad7,bitRead(value,7));
  //delayMicroseconds(1);
  //finish write, latch data
  digitalWrite(rw,HIGH);
  //delayMicroseconds(1);
}

boolean adjust(byte address){
 
          //read current value
          byte value=0;
          byte b;
          if ( (address<0) || (address > 10)) return false;
          
           if (!bitRead(readbyte(regA),7)) value = readbyte(address);
          b = readbyte(regB);
          //set SET bit of register B that will prevent double buffer update from internal buffer
          b=b|0x80;
          writebyte(regB,b);
           
           if (bitRead(readbyte(regB),7))        
          {//start upd
            
          switch (address){
          
          case 0:
          //seconds
              writebyte(address,0); //min
          break; 
          
          case 1:
          //seconds alarm
          if (value == 59) {writebyte(address,0);}
          else {
              value++; 
              writebyte(address,value); //min
              }
          break;
          
          case 2:
          //minutes
          if (value == 59) {writebyte(address,0);}
          else {
             value++; 
              writebyte(address,value); //min
              }  
          break;
          
          case 3:
          //minutes alarm
          if (value == 59) {writebyte(address,0);}
          else {
             value++; 
              writebyte(address,value); //min
              }  
          break;
          
          case 4:
          //hours
          if (value == 23) {writebyte(address,0);}
          else {
             value++; 
              writebyte(address,value); //min
              }  
          break;
         case 5:
          //hours alarm
          if (value == 23) {writebyte(address,0);}
          else {
             value++; 
              writebyte(address,value); //min
              }  
          break;
         
         case 6:
          //day of week
          if (value == 7) {writebyte(address,1);}
          else {
             value++; 
              writebyte(address,value); //min
              }  
          break;
          case 7:
          //day of month, this must be modified in future!!!!
          if (value == 31) {writebyte(address,1);}
          else {
             value++; 
              writebyte(address,value); //min
              }  
          break;
          
         case 8:
          //month
          if (value == 12) {writebyte(address,1);}
          else {
             value++; 
              writebyte(address,value); //min
              }  
          break;
          case 9:
          //year
          if (value == 99) {writebyte(address,0);}
          else {
             value++; 
              writebyte(address,value); //min
              }  
          break;
//        default:
                }//end switch
          }//end upd
          
          //mask regA and clear SET bit
          b=b&0x7F;
          writebyte(regB,b);
      return true;
  
}