Digital clock using RTC DS12C887 and 8051 microcontroller (AT89C51) with time set

Real time clock (RTC) is widely used in many application to provide accurate time. This article explains the making of a simple digital clock using RTC DS12C887 and 8051 microcontroller (AT89C51). The output is displayed on an LCD. This clock also has a provision of setting time at any instant. The clock uses the concept of our earlier articles of interfacing RTC DS12C887 with microcontroller. The clock described here uses the method of polling for running. For further details on interfacing RTC DS12C887 with AT89C51 using polling, refer RTC interfacing. The free source code for the program is available in C.

The circuit diagram shows the connection of RTC with the microcontroller. Port P2 is used as data port for LCD; port P0 of the microcontroller is used as data port of RTC DS12C887. The pins P1^0, P1^1, P1^2, P1^3, P1^4, P1^5, P1^6 of controller AT89C51 are configured as reset, rs, rw, e, dig_hr1, dig_min1, start pins respectively.

In this clock the RTC is used in 24 hour mode which gives accurate time and can be displayed on LCD through microcontroller. Firstly oscillator is set, than RTC is set in 24 hour mode by setting 0X20 in register A. For more details, refer RTC interfacing with AT89C51.

The microcontroller continuously reads the data from the RTC. The algorithm processes the data and displays the data in correct order on the LCD screen. Interrupt 2 of the microcontroller is used to set time. Whenever P3^3 pin is made low (0), interrupt2 comes and set_time function is called for setting the time. Hours can be set by using the dig_hr1 pin. Minutes can be set with the dig_min1 pin. After setting the time, start pin is made high and the clock starts with the time set by user.

Project Source Code

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//Program for Digital clock using RTC DS12C887 and 8051 microcontroller (AT89C51) with time set
/*24 hr clock
set p3^3=0,then start=0 then set time by dig_hr1 & dig_min1, then remove p3^3 & start	*/
#include<reg51.h>
#include<absacc.h>
#define dataport P2
#define port P1
#define lcdport P3
 sbit reset = port^0;
 sbit rs =port^1;
 sbit rw =port^2;
 sbit e = port^3;
 sbit dig_hr1=port^4;
 sbit dig_min1=port^5;
 sbit start=port^6;
 int  min1=0,hr1=0;
 int min0=60,hr0=25;
 unsigned char temp=60,hr,min,sec,num[60]={0x00,0x01,0x02,0x03,0x04,0x05,0x06,0x07,0x08,0X09,0X10,0X11,0X12,0X13,0X14,0X15,0X16,0X17,0X18,0X19,0X20,0X21,0X22,0X23,0X24,0X25,0X26,0X27,0X28,0X29,0X30,0X31,0X32,0X33,0X34,0X35,0X36,0X37,0X38,0X39,0X40,0X41,0X42,0X43,0X44,0X45,0X46,0X47,0X48,0X49,0X50,0X51,0X52,0X53,0X54,0X55,0X56,0X57,0X58,0X59};

 void delay(unsigned int msec )
{
	int i ,j ;
	for(i=0;i<msec;i++)
	for(j=0; j<1275; j++);
}

void lcd_cmd(unsigned char item)
{
	dataport = item;
	rs= 0;
	rw=0;
	e=1;
	delay(1);
	e=0;
	return;
} 

// function to send data
void lcd_data(unsigned char item)
{
	dataport = item;
	rs= 1;
	rw=0;
	e=1;
	delay(1);
	e=0;
	return;
}

void lcd_data_string(unsigned char *str)
{
	int i=0;
	while(str[i]!='')
	{
		lcd_data(str[i]);
		i++;
		delay(1);
	}
	return; 
}

lcd_data_int(int time_val)
{
	int int_amt;
	int_amt=time_val/10;
	lcd_data(int_amt+48);
	int_amt=time_val%10;	 
	lcd_data(int_amt+48);
}


void lcd()
{
	lcd_cmd(0x38);		   
	delay(5);
	lcd_cmd(0x0C);        
	delay(5);
	lcd_cmd(0x80);
	delay(5);
}

void set_rtc_time()  
{
	XBYTE[10]=0x20;
	XBYTE[11]=0x82;
	XBYTE[0]=0x00;
	XBYTE[2]=min;
	XBYTE[4]=hr;
	XBYTE[7]=0x01;
	XBYTE[8]=0x01;
	XBYTE[9]=0x10;
	XBYTE[1]=0xFF;
	XBYTE[3]=0xFF;
	XBYTE[5]=0xFF;
	XBYTE[11]=0x22;
}

void set_hr1()
{
	hr1++;
	if(hr1>23)
	hr1=0;
	lcd_cmd(0xc3);
	lcd_data_int(hr1);
	lcd_data(':');
	hr0=hr1;
}

void set_min1()
{
	min1++;
	if(min1>59)
	min1=0;
	lcd_cmd(0xc6);
	lcd_data_int(min1);
	min0=min1;
}

void set_time()	interrupt 2
{
	lcd_cmd(0x01);
	if(start==0)
	{
		lcd_data_string("SET TIMING");
		lcd_cmd(0xc3);
		lcd_data_int(hr1);
		lcd_data(':');
		lcd_data_int(min1);
		while(start==0)
		{
			delay(10);
			if(dig_hr1==0)
			set_hr1();
			if(dig_min1==0)
			set_min1();	 
		}
	}
	lcd_cmd(0x01);
	hr=num[hr1];
	min=num[min1];
	set_rtc_time();
	lcd_cmd(0x80);
	lcd_data_string("TIME:");
	hr0=25;
	min0=60;
}

bcdconv(unsigned char mybyte)
{
	unsigned char x,y;
	x=	mybyte & 0x0F;
	x=x | 0x30;
	y= mybyte & 0xF0;
	y=y>>4;
	y=y | 0x30;
	lcd_data(y);
	lcd_data(x);
}

void read_rtc_display() 
{ 
	reset=0;
	reset=1;
	XBYTE[11]=0x02;
	hr=XBYTE[4];
	lcd_cmd(0x87);
	min=XBYTE[2];
	sec=XBYTE[0];
	if(hr!=hr0)
	{
		lcd_cmd(0X87);
		bcdconv(hr);
		lcd_data(':');
		hr0=hr;
	}
	if(min!=min0)
	{
		lcd_cmd(0X8A);
		bcdconv(min);
		lcd_data(':');
		min0=min;
	}
	if(sec!=temp)
	{
		lcd_cmd(0x8D);
		bcdconv(sec);
		temp=sec;
	}
}

void main()
{
	reset=1;
	lcd();
	XBYTE[10]=0x20;
	XBYTE[1]=0xFF;
	XBYTE[3]=0xFF;
	XBYTE[5]=0xFF;
	XBYTE[11]=0x02;
	lcd_cmd(0x01);
	IE=0x84;
	lcd_cmd(0x80);
	lcd_data_string("TIME:");
	while(1)
	{
		read_rtc_display();
	}
}

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