68 lines
2.2 KiB
C
68 lines
2.2 KiB
C
#include "msp430.h"
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#define TXD BIT2
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#define RXD BIT1
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#define TRIG BIT4
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#define ECHO BIT6
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#define CM 58
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unsigned int TXByte;
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void main(void) {
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WDTCTL = WDTPW + WDTHOLD; // Stop WDT
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BCSCTL1 = CALBC1_1MHZ; // Set range
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DCOCTL = CALDCO_1MHZ;
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BCSCTL2 &= ~(DIVS_3); // SMCLK = DCO = 1 MHz
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P1SEL = BIT1 + BIT2; // P1.1 = RXD, P1.2=TXD
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P1SEL2 = BIT1 + BIT2; // P1.1 = RXD, P1.2=TXD
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UCA0CTL1 |= UCSSEL_2; // Use SMCLK
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UCA0BR0 = 104; // Set baud rate to 9600 with 1MHz clock (Data Sheet 15.3.13)
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UCA0BR1 = 0; // Set baud rate to 9600 with 1MHz clock
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UCA0MCTL = UCBRS0; // Modulation UCBRSx = 1
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UCA0CTL1 &= ~UCSWRST; // Initialize USCI state machine
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P1DIR |= TXD;
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P1OUT |= TXD;
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P1DIR |= TRIG; // set trigger output
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P1DIR &= ~ECHO; // set echo input
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P1IE |= ECHO; // use echo input as interrupt
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TACTL = TACLR; // reset clock
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TACTL = TASSEL_2 | MC_2; // set SMCLK timer to count up at 1 MHz
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__enable_interrupt();
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while (1) {
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P1OUT |= TRIG; // start trigger signal
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__delay_cycles(10); // we need a >10 us pulse and one clock cycle is 1 us
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P1OUT &= ~TRIG; // end trigger signal
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P1IES &= ~ECHO; // interrupt on low to high
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__bis_SR_register(LPM0_bits + GIE);
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TAR = 0;
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P1IES |= ECHO; // interrupt on high to low
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__bis_SR_register(LPM0_bits + GIE);
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TXByte = TAR / CM; // distance in cm
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TXByte = (TXByte <= 0xFF) * TXByte; // set to 0 if beyond range
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while (!(IFG2 & UCA0TXIFG)); // wait for TX buffer to be ready for new data
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UCA0TXBUF = TXByte;
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__delay_cycles(100000); // wait >10 ms before measuring again
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}
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}
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#if defined(__TI_COMPILER_VERSION__)
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#pragma vector=PORT1_VECTOR
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__interrupt void port1_isr(void)
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#else
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void __attribute__ ((interrupt(PORT1_VECTOR))) port1_isr (void)
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#endif
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{
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P1IFG = 0;
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__bic_SR_register_on_exit(LPM0_bits); // take us out of low power mode
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} |