Below is the code:
#include "msp430.h"
#define TRIG_PIN BIT1 // Corresponds to P2.1
#define ECHO_PIN BIT1 // Corresponds to P1.1
//#define TXD BIT2 // TXD on P1.2
volatile unsigned long start_time;
volatile unsigned long end_time;
volatile unsigned long delta_time;
volatile unsigned long distance;
void wait_ms(unsigned int ms)
{
unsigned int i;
for (i = 0; i <= ms; i++)
{
__delay_cycles(1000);
}
}
#if defined(__TI_COMPILER_VERSION__)
#pragma vector = TIMER0_A0_VECTOR
__interrupt void ta1_isr(void)
#else
void __attribute__((interrupt(TIMER0_A0_VECTOR))) ta1_isr(void)
#endif
{
switch (TAIV)
{
//Timer overflow
case 10:
break;
//Otherwise Capture Interrupt
default:
// Read the CCI bit (ECHO signal) in CCTL0
// If ECHO is HIGH then start counting (rising edge)
if (CCTL0 & CCI)
{
start_time = CCR0;
} // If ECHO is LOW then stop counting (falling edge)
else
{
end_time = CCR0;
delta_time = end_time - start_time;
distance = (unsigned long)(delta_time / 0.00583090379);
//set a range
if (distance / 10000 >= 2.0 && distance / 10000 <= 10)
{
//turn on LED P1.0;
P1OUT |= BIT0;
}
else
P1OUT &= ~BIT0;
}
break;
}
TACTL &= ~CCIFG; // reset the interrupt flag
}
void reset_timer(void)
{
//Clear timer
TACTL |= TACLR;
}
void main(void)
{
// Stop Watch Dog Timer
WDTCTL = WDTPW + WDTHOLD;
// Set ECHO (P1.1) pin as INPUT
P1DIR &= ~ECHO_PIN;
// Set P1.1 as CCI0A (Capture Input signal).
P1SEL |= ECHO_PIN;
// Set TRIGGER (P2.1) pin as OUTPUT
P2DIR |= TRIG_PIN;
// Set TRIGGER (P2.1) pin to LOW
P2OUT &= ~TRIG_PIN;
P1DIR |= BIT0;
P1OUT &= ~BIT0;
//P1DIR |= BIT6;
/* Use internal calibrated 1MHz clock: */
BCSCTL1 = CALBC1_1MHZ; // Set range
DCOCTL = CALDCO_1MHZ;
BCSCTL2 &= ~(DIVS_3); // SMCLK = DCO = 1MHz
// Stop timer before modifying the configuration
TACTL = MC_0;
CCTL0 |= CM_3 + SCS + CCIS_0 + CAP + CCIE;
// Select SMCLK with no divisions, continuous mode.
TACTL |= TASSEL_2 + MC_2 + ID_0;
// Global Interrupt Enable
__enable_interrupt();
while (1)
{
// send ultrasonic pulse
reset_timer();
// Enable TRIGGER
P2OUT |= TRIG_PIN;
// Send pulse for 10us
__delay_cycles(10);
// Disable TRIGGER
P2OUT &= ~TRIG_PIN;
// wait 500ms until next measurement
wait_ms(500);
}
}
