Digital clock using DS12C887 and 8051 microcontroller (AT89C51) in 12 hour mode

This article is an improved version of LCD based clock using RTC DS12C887 and 8051 microcontroller (AT89C51) using update interrupt. DS12C887 has two modes of operation i.e., 12 hour and 24 hour mode. In our earlier articles we explained how to use 24 hour mode. This article explores how we can use the 12 hour mode of RTC. This is done by making a clock using RTC and 8051 microcontroller (AT89C51) with 12 hour mode operation. The clock time is displayed on a 16x2 LCD interface. 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 while port P0 of the microcontroller AT89C51 is used as data port for the RTC DS12C887. The pins P1^0 – P1^7 of the microcontroller are configured as reset, rs, rw, e, dig_hr1, dig_min1, start, setmode, am_pm pins respectively.

Clock principally works on two modes. In the 24 hour mode hours are counted from 0 to 23 and in the 12 hour mode hours are counted from 0 to 11. In the 12 hour mode the RTC returns the BCD value 1-12 for AM and 81-92 for PM. The RTC returns the BCD value 1 for 1 AM.

The values corresponding to the output 1 to 12 i.e., 0 to 11 are stored in an array nummin. An array numhr is used to store the values from 81 to 92. When RTC sends the output, microcontroller reads hours and if it matches with any of the numhr variable it displays corresponding value from nummin array else it displays the same value for hours. This trick is used to convert the RTC from 24 hour mode to 12 hour mode.

Interrupt 0 of controller is used to get time by update interrupt. Interrupt 2 is used for setting the time. 24 hour mode can be used as explained in LCD based clock using RTC DS12C887 and 8051 microcontroller (AT89C51) using update interrupt.

Project Source Code

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//Program for Digital clock using DS12C887 & 8051 microcontroller (AT89C51) in 12 hour mode
/*12hr clock
set p3^3=0,then start=0 them set time by dig_hr1 & dig_min1, then remove p3^3 & start
am:p1^7=0	 pm:p1^7=1*/

#include<reg51.h>
#include<absacc.h>
#define dataport P2
#define port P1

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;
sbit setmodeam_pm=port^7;

int hr1=0;
int min1=0;
int modeam_pm=0,q,am_pm;
unsigned char numhr[12]={0x81,0X82,0X83,0X84,0X85,0X86,0X87,0X88,0X89,0X90,0X91,0X92};
unsigned char temp,hr,min,sec,nummin[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;
}
 
// DATA SENDING FUNCTION
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()			// Function to intitialize LCD
{
	lcd_cmd(0x38);		  
	delay(5);
	lcd_cmd(0x0F);        
	delay(5);
	lcd_cmd(0x80);
	delay(5);
}

void set_rtc_time()  
{
	if(modeam_pm==2)
	{
		hr=numhr[hr1];
	}
	XBYTE[10]=0x20;
	XBYTE[11]=0x80;
	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]=0x20;
}

void set_hr1()
{
	hr1++;
	if(hr1>11)
	hr1=0;
	lcd_cmd(0xc3);
	lcd_data_int(hr1);
	lcd_data(':');
}

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


void set_time()	interrupt 2	   //Time set function
{
	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();
			if(setmodeam_pm==0)	 
			{
				modeam_pm=1;
			}
			else
			{
				modeam_pm=2;
			}
		}
	}
	lcd_cmd(0x01);
	hr=nummin[hr1];
	min=nummin[min1];
	set_rtc_time();
}

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() interrupt 0			//Alarm interrupt
{ 
	lcd_cmd(0x01);
	lcd_cmd(0x80);
	lcd_data_string("TIME:");
	lcd_cmd(0X86);
	reset=0;
	reset=1;
	XBYTE[11]=0x10;
	hr=XBYTE[4];
	temp=0x87;
	for(q=0;q<12;q++)
	if(hr==numhr[q])
	{
		hr=nummin[q+1];
		am_pm=2;
		if(q==11)
		hr=0x00;
	}
	else
	am_pm=1;
	bcdconv(hr);
	lcd_data(':');
	min=XBYTE[2];
	bcdconv(min);
	lcd_data(':');
	sec=XBYTE[0];
	bcdconv(sec);
	if(am_pm==1)
	{
		lcd_data_string("am");
	}
	else
	{
		lcd_data_string("pm");
	}
}

void main()
{
	setmodeam_pm=0;
	setmodeam_pm=1;
	reset=1;
	lcd();
	XBYTE[10]=0x20;
	XBYTE[11]=0x10;
	lcd_cmd(0x01);
	IE=0x85;
	while(1);
}

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