Following the configuration details as in question #25, we want to toggle a LED at around 100 milliseconds interval. assume the led is connected to RA3. Write a C application to do so.

Question

question 25:
Timer1 uses the interval clock with 1:64 prescaling. The microcontroller uses primary oscillator with frequency 2.875 MHz as the clock source. it also utilizes PLL. if PR1 = 1000, then at what interval the interrupt with priority 3 will be generated? show your work.

Answer 1

To calculate the interval at which the interrupt with priority 3 will be generated, we need to determine the timer period using the given information.

The primary oscillator frequency is given as 2.875 MHz, and it is stated that the microcontroller utilizes PLL. However, the question does not provide the details of the PLL configuration (e.g., multiplication factor), which are needed to determine the final clock frequency. Therefore, we cannot accurately calculate the timer period without this information.

Assuming the PLL is configured to multiply the primary oscillator frequency by a known factor (e.g., 4, 8, 16, etc.), we can use the following formula to calculate the timer period:

Timer Period (TMR) = (PR1 + 1) * Prescaler * Tcy

Where Tcy is the instruction cycle time in seconds.

However, since the question does not provide the necessary information about the PLL configuration, it is not possible to determine the exact timer period and therefore the interval at which the interrupt with priority 3 will be generated.

Answer 2

What is the c programming code?

Answer 3

Here's the updated C programming code to toggle an LED at around 100 milliseconds interval on pin RA3 using Timer1 interrupt:

```c
#include <xc.h>

// Configuration bits
#pragma config FOSC = HSPLL // Primary Oscillator (HS w/ PLL)
#pragma config PLLDIV = 2 // PLL Prescaler (Divide by 2)
#pragma config CPUDIV = OSC1_PLL2 // CPU Division (Use 1:2 CPU divider)
#pragma config WDTEN = OFF // Watchdog Timer (Disabled)
#pragma config MCLRE = ON // Master Clear Pin (Enabled)

// Function prototypes
void init(void);
void __interrupt(high_priority) Timer1Interrupt();

// Global variables
volatile unsigned int counter = 0;

int main(void) {
init();

while(1) {
// Loop indefinitely
}

return 0;
}

void init(void) {
// Configure Timer1
T1CONbits.TMR1CS = 0; // Timer1 uses internal clock (Fosc/4)
T1CONbits.T1CKPS = 0b10; // 1:64 prescaler
T1CONbits.TMR1ON = 1; // Enable Timer1

// Set up Timer1 interrupt
PIE1bits.TMR1IE = 1; // Enable Timer1 interrupt
INTCONbits.PEIE = 1; // Enable peripheral interrupts
INTCONbits.GIE = 1; // Enable global interrupts

// Configure RA3 as output
TRISAbits.RA3 = 0;
}

void __interrupt(high_priority) Timer1Interrupt() {
// Check if Timer1 overflowed
if (PIR1bits.TMR1IF) {
PIR1bits.TMR1IF = 0; // Clear Timer1 interrupt flag

counter++; // Increment counter

// Toggle LED on RA3
if (counter >= 781) { // Toggle every 100ms (100ms / (1.28us * 64 * 256))
counter = 0; // Reset counter
LATAbits.LATA3 ^= 1; // Toggle LED on RA3
}
}
}
```

In this code, we have updated the interval calculation to account for the instruction cycle time which is approximately 1.28 microseconds, based on a 2.875 MHz clock frequency.

The counter is incremented in each Timer1 interrupt and checked against 781 (100 ms / (1.28 us * 64 * 256)) to determine when to toggle the LED on pin RA3. When the counter exceeds 781, it is reset to 0 and the LED state is toggled.

Please note that the calculations and values provided assume a specific clock frequency and prescaler value. If different values or configurations are used, the calculations and comparisons may need to be adjusted accordingly.