timer_500mS

Code Breakdown:

1. Preprocessor Directives:

• #include <pic.h>: Includes the header file pic.h, which contains definitions and declarations specific to PIC microcontrollers.

2. Variable Declarations:

• unsigned char count = 0;: Declares an unsigned character variable count and initializes it to 0. This variable is used to keep track of the number of 50ms intervals that have elapsed.

3. main() Function:

• Initialization:

  • TRISC = 0;: Configures PORTC as output pins.
  • PORTC = 0;: Clears the output pins on PORTC.
  • T0CS = 0;: Selects the internal clock source (Fosc/4) for TMR0.
  • PSA = 0;: Assigns the prescaler to TMR0.
  • PS2 = 1; PS1 = 1; PS0 = 1;: Sets the prescaler to 256, providing a timer tick every 50 milliseconds.
  • TMR0 = 61;: Initializes TMR0 with the value 61 to generate a 50ms delay.
  • RC0 = 1;: Sets the output on RC0.

• Main Loop:

  • while (1) { ... }: The main loop continues indefinitely.
  • Interrupt Handling:
    • if (T0IF) { ... }: Checks if the TMR0 interrupt flag is set.
    • TMR0 = 61;: Reloads TMR0 with the value 61 to start another 50ms delay.
    • count++;: Increments the count variable.
    • if (count == 20) { ... }: Checks if 20 50ms intervals have elapsed (1 second).
      • RC0 = !RC0;: Toggles the RC0 output.
      • count = 0;: Resets the count variable to 0.
    • T0IF = 0;: Clears the TMR0 interrupt flag.

Explanation:

The code implements a simple blinking LED circuit that toggles an output pin (RC0) every second. The main components of the code are:

• Timer Initialization: TMR0 is configured as an internal timer with a prescaler of 256, providing a timer tick every 50 milliseconds.
• Interrupt Handling: The TMR0 interrupt is used to increment a counter and toggle the output pin after 20 50ms intervals (1 second).

#include <pic.h>
unsigned char count=0;

void main()

{
TRISC=0;    // PORTC output
PORTC=0;   

T0CS=0;        // Internal Mode (Fosc/4)
PSA=0;        // Prescaler assigned to TMR0
PS2=1;
PS1=1;
PS0=1;   
   
TMR0=61;    // (256-195=61) for 50mS time
RC0=1;        // output on


while(1)   
{
    if(T0IF==1){
    TMR0=61;
    count++;
        if (count==20){

        RC0=!RC0; // RC0 toggle
        count=0;
        }   

    T0IF=0;
    }
}
}