Components required
- 8051 Microcontroller (89C51)
- Resistor – 10K
- Capacitor – 10uF, 33pF (two)
- Crystal oscillator – 12MHz
- LCD display.
Circuit diagram
[caption id="" align="aligncenter" width="490"]Digital Stopwatch using 8051 Microcontroller[/caption]
Pin description of LCD display
[caption id="" align="aligncenter" width="341"]LCD pin diagram[/caption]
| Pinnumber | Name | Description |
| 1 | Vss | Ground |
| 2 | Vdd | +5V |
| 3 | Vee | Contrast Adjustment -2V to -5V |
| 4 | RS | Register Select |
| 5 | RW | 1 -Read, 0-Write |
| 6 | E | Enable Strobe |
| 7 | D0 | Data Line |
| 8 | D1 | Data Line |
| 9 | D2 | Data Line |
| 10 | D3 | Data Line |
| 11 | D4 | Data Line |
| 12 | D5 | Data Line |
| 13 | D6 | Data Line |
| 14 | D7 | Data Line |
| 15 | LED+ | Backlit LED +V Vdd (Optional signal) |
| 16 | LED- | Backlit LED +V Vdd (Optional signal) |
C program
// ************************************************
// Project: Digital Stopwatch using 8051 microcontroller
// Author: Mayuresh Joshi
// Blog: myclassbook.org
// ************************************************
#include<reg51.h>
//Function declarations
void cct_init(void);
void delay(int);
void lcdinit(void);
void WriteCommandToLCD(int);
void WriteDataToLCD(char);
void ClearLCDScreen(void);
void InitTimer0(void);
void UpdateTimeCounters(void);
void DisplayTimeToLCD(unsigned int,unsigned int,unsigned int);
//*******************
//Pin description
/*
P2.4 to P2.7 is data bus
P1.0 is RS
P1.1 is E
*/
//********************
// Defines Pins
sbit RS = P1^0;
sbit E = P1^1;
// Define Clock variables
unsigned int usecCounter = 0;
unsigned int msCounter = 0;
unsigned int secCounter = 0;
unsigned int minCounter = 0;
unsigned int hrCounter = 0;
// ***********************************************************
// Main program
//
void main(void)
{
cct_init(); // Make all ports zero
lcdinit(); // Initilize LCD
InitTimer0(); // Start Timer0
while(1)
{
if( msCounter == 0 ) // msCounter becomes zero after exact one sec
{
DisplayTimeToLCD(hrCounter, minCounter, secCounter); // Displays time in HH:MM:SS format
}
UpdateTimeCounters(); // Update sec, min, hours counters
}
}
void cct_init(void)
{
P0 = 0x00; //not used
P1 = 0x00; //not used
P2 = 0x00; //used as data port
P3 = 0x00; //used for generating E and RS
}
void InitTimer0(void)
{
TMOD &= 0xF0; // Clear 4bit field for timer0
TMOD |= 0x02; // Set timer0 in mode 2
TH0 = 0x05; // 250 usec reloading time
TL0 = 0x05; // First time value
ET0 = 1; // Enable Timer0 interrupts
EA = 1; // Global interrupt enable
TR0 = 1; // Start Timer 0
}
void Timer0_ISR (void) interrupt 1 // It is called after every 250usec
{
usecCounter = usecCounter + 250; // Count 250 usec
if(usecCounter==1000) // 1000 usec means 1msec
{
msCounter++;
usecCounter = 0;
}
TF0 = 0; // Clear the interrupt flag
}
void UpdateTimeCounters(void)
{
if (msCounter==1000)
{
secCounter++;
msCounter=0;
}
if(secCounter==60)
{
minCounter++;
secCounter=0;
}
if(minCounter==60)
{
hrCounter++;
minCounter=0;
}
if(hrCounter==24)
{
hrCounter = 0;
}
}
void DisplayTimeToLCD( unsigned int h, unsigned int m, unsigned int s ) // Displays time in HH:MM:SS format
{
ClearLCDScreen(); // Move cursor to zero location and clear screen
// Display Hour
WriteDataToLCD( (h/10)+0x30 );
WriteDataToLCD( (h%10)+0x30 );
//Display ':'
WriteDataToLCD(':');
//Display Minutes
WriteDataToLCD( (m/10)+0x30 );
WriteDataToLCD( (m%10)+0x30 );
//Display ':'
WriteDataToLCD(':');
//Display Seconds
WriteDataToLCD( (s/10)+0x30 );
WriteDataToLCD( (s%10)+0x30 );
}
void delay(int a)
{
int i;
for(i=0;i<a;i++); //null statement
}
void WriteDataToLCD(char t)
{
RS = 1; // This is data
P2 &= 0x0F; // Make P2.4 to P2.7 zero
P2 |= (t&0xF0); // Write Upper nibble of data
E = 1; // => E = 1
delay(150);
E = 0; // => E = 0
delay(150);
P2 &= 0x0F; // Make P2.4 to P2.7 zero
P2 |= ((t<<4)&0xF0);// Write Lower nibble of data
E = 1; // => E = 1
delay(150);
E = 0; // => E = 0
delay(150);
}
void WriteCommandToLCD(int z)
{
RS = 0; // This is command
P2 &= 0x0F; // Make P2.4 to P2.7 zero
P2 |= (z&0xF0); // Write Upper nibble of data
E = 1; // => E = 1
delay(150);
E = 0; // => E = 0
delay(150);
P2 &= 0x0F; // Make P2.4 to P2.7 zero
P2 |= ((z<<4)&0xF0);// Write Lower nibble of data
E = 1; // => E = 1
delay(150);
E = 0; // => E = 0
delay(150);
}
void lcdinit(void)
{
///////////// Reset process from datasheet /////////
delay(15000);
P2 &= 0x0F; // Make P2.4 to P2.7 zero
P2 |= (0x30&0xF0); // Write 0x3
E = 1; // => E = 1
delay(150);
E = 0; // => E = 0
delay(150);
delay(4500);
P2 &= 0x0F; // Make P2.4 to P2.7 zero
P2 |= (0x30&0xF0); // Write 0x3
E = 1; // => E = 1
delay(150);
E = 0; // => E = 0
delay(150);
delay(300);
P2 &= 0x0F; // Make P2.4 to P2.7 zero
P2 |= (0x30&0xF0); // Write 0x3
E = 1; // => E = 1
delay(150);
E = 0; // => E = 0
delay(150);
delay(650);
P2 &= 0x0F; // Make P2.4 to P2.7 zero
P2 |= (0x20&0xF0); // Write 0x2
E = 1; // => E = 1
delay(150);
E = 0; // => E = 0
delay(150);
delay(650);
/////////////////////////////////////////////////////
WriteCommandToLCD(0x28); //function set
WriteCommandToLCD(0x0c); //display on,cursor off,blink off
WriteCommandToLCD(0x01); //clear display
WriteCommandToLCD(0x06); //entry mode, set increment
}
void ClearLCDScreen(void)
{
WriteCommandToLCD(0x01); // Clear screen command
delay(1000);
}
Download
Click here to download C program, Proteus simulation file, HEX file, etc.
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