How to display voltages on LCD of a PIC16F877A embedded system?

Question

I am writing code to display voltage data on the LCD on a PIC16F877A. To observe the values on the display, it needs a delay but when I use the delay function, it gets stuck. When I change the pot value, it will not show during the observation delay. So I need assistance and guidance to introduce delay. When I change the value of the pot, I should change it during a 5 second delay. I share my code below:

// Lcd pinout settings
sbit LED1 at RB4_bit;
sbit LCD_RS at RD2_bit;
sbit LCD_EN at RD3_bit;
sbit LCD_D4 at RD4_bit;
sbit LCD_D5 at RD5_bit;
sbit LCD_D6 at RD6_bit;
sbit LCD_D7 at RD7_bit;
//sbit SW at RB1_bit;
// Pin direction
sbit LCD_RS_Direction at TRISD2_bit;
sbit LCD_EN_Direction at TRISD3_bit;
sbit LCD_D4_Direction at TRISD4_bit;
sbit LCD_D5_Direction at TRISD5_bit;
sbit LCD_D6_Direction at TRISD6_bit;
sbit LCD_D7_Direction at TRISD7_bit;


unsigned short count,pls;
unsigned char ch,bh;
long tlong,blong;

void adc1_config();
void adc2_config();
int adc1_prcs();
int adc2_prcs();

void main()
{
adc1_config();
adc2_config();
ADC_Init();
Lcd_Init();
Lcd_Cmd(_LCD_CLEAR);
Lcd_Cmd(_LCD_CURSOR_OFF);
adc1_prcs();
adc2_prcs();
Lcd_Out(1,1,"VAC-IN : ");
Lcd_Out(2,1,"VAC-OUT: ");
delay_ms(5000);
// here i want delay to adjust input voltage and calibrate.
// delay does not work here bcoz adc value stuck due to delay function.
// suugest proven technique to avoid delay.
TRISB.F4 = 0;
while(1)
{
Lcd_Out(1,1,"info page");
Lcd_Out(2,4,"123456789");
delay_ms(5000);
//same scenario occur here
Lcd_Cmd(_LCD_CLEAR);
adc1_prcs();
adc2_prcs();
Lcd_Out(1,1,"VAC-IN : ");
Lcd_Out(2,1,"VAC-OUT: ");
delay_ms(5000);
Lcd_Cmd(_LCD_CLEAR);
 // and here also

 }
}

I tried using the mikroC compiler.

Answer 1

Your code needs to avoid delay altogether - during a delay without multi-threading support, the CPU stalls doing no useful work (unless performed in interrupt handlers). One solution to that (short of an RTOS) is rather than delay, simply poll a free-running counter of elapsed_time and perform actions whatever they become " due ".

I am no PIC developer and I have synthesised the following from information on various sites - it may not be correct and most of it was for Microchip's XC8 compiler and may need some changes for MikroC - I think they have a different naming convention for peripheral register access structures.

So given the following 1ms tick implementation using TIMER 0:

#define FOSC_FREQ 4000000  //4MHz

// 1/1000 seconds 24=56 prescaler
#define TIMER_1MS (256 - FOSC_FREQ / (1024 * 1000) ) 

static volatile uint32_t ms_tick = 0 ;
uint32_t initMsTick()
{
    OPTION_REGbits.PSA = 0; 
    OPTION_REGbits.PS = 0b111;  //Set the prescaler to 1:256
    OPTION_REGbits.T0CS = 0;
    INTCONbits.T0IF = 0;        //Clear the Timer 0 interrupt flag
    TMR0 = TIMER_1MS;           //Load counter for 1ms tick
    INTCONbits.T0IE = 1;        //Enable the Timer 0 interrupt
    INTCONbits.GIE = 1;         //Set the Global Interrupt Enable
}

uint32_t getMsTick()
{
    uint32_t now = ms_tick ;
    while( now != ms_tick )
    {
        now = ms_tick ;
    }
    return now ;
}

void interrupt()
{
    if( INTCONbits.T0IF) 
    {
        INTCONbits.T0IF = TIMER_1MS ;
        ms_tick++ ;
    }
}

you might then create a timer interface thus:

#include <stdbool.h>

typedef struct
{
    uint32_t ref ;
    uinr32_t period ;
} timer_t ;

void startTimer( timet_t* timer, uint32_t period )
{
    timet->ref = getMsTick() ;
    timer->period = period ;
}

bool hasTimerExpired( timer_t* timer )
{
    return (getMsTick() - timer->ref) >= timer->period ;
}

Then in your application for example:

    adc1_config();
    adc2_config();
    ADC_Init();
    Lcd_Init();
    Lcd_Cmd(_LCD_CURSOR_OFF);

    TRISB.F4 = 0;
    
    timer_t display_time ;
    for(;;)
    {
        Lcd_Cmd(_LCD_CLEAR);
        Lcd_Out(1,1,"VAC-IN : ");
        Lcd_Out(2,1,"VAC-OUT: ");
        startTimer( &display_time, 4000u ) ;
        while( !hasTimerExpired( &display_time ) )
        {
            adc1_prcs();
            adc2_prcs();
        }

        Lcd_Cmd(_LCD_CLEAR);
        Lcd_Out(1,1,"info page");
        Lcd_Out(2,4,"123456789");
        timer_t display_time ;
        startTimer( &display_time, 4000u ) ;
        while( !hasTimerExpired( &display_time ) )
        {
            adc1_prcs();
            adc2_prcs();
        }
    }

Note that I have removed your unnecessary initial display by making it the first display in the loop. It may have been there for a reason, but I cannot see it.

This can be simplified given:

void displayPage( int page )
{
    Lcd_Cmd(_LCD_CLEAR);
    switch( page )
    {
        case 0 :
        {
            Lcd_Out(1,1,"VAC-IN : ");
            Lcd_Out(2,1,"VAC-OUT: ");
        } 
        break ;

        case 1 :
        {
            Lcd_Out(1,1,"info page");
            Lcd_Out(2,4,"123456789");
        }
        break ;
    }
}

then

    int page = 0 ;
    displayPage( page ) ;
    timer_t display_time ;
    startTimer( &display_time, 4000u ) ;

    for(;;)
    {
        // Read ADCs continuously
        adc1_prcs();
        adc2_prcs();

        // Every four seconds flip display
        if( hasTimerExpired( &display_timer ) )
        {
            startTimer( &display_time, 4000u )
            page = page == 0 ? 1 : 0 ;
            displayPage( page ) ;
        }
    }

Note that the timer interface allows multiple concurrent timers of differing expiry periods so that you can have code like:

#define TASK1_PERIOD 1000u ; // 1 second
#define TASK2_PERIOD  333u ; // 1/3 second

timet_t t1, t2 ;
startTimer( &t1, TASK1_PERIOD ) ; 
startTimer( &t2, TASK2_PERIOD ) ;  // 1/3 second

for(;;)
{
    if( hasTimerExpired( &t1 ) )
    {
        startTimer( &t1, TASK1_PERIOD ) ; // restart
        
        // Things to do every second here... 
    }

    if( hasTimerExpired( &t2 ) )
    {
        startTimer( &t2, TASK2_PERIOD ) ; // restart
        
        // Things to do every 1/3 second here... 
    }

    // Things to do continuously here...
}

The architecture lends itself to implementing time-triggered state-machines, and periodic single-shot functions.