nicholasjconn · June 7, 2011 18:20 · Jun 7, 2011
diff --git a/LaunchPad_DAC.c b/LaunchPad_DAC.c
@@ -0,0 +1,99 @@
+/************************************************************************
+ *                       NJC's Simple LaunchPad DAC
+ * 
+ * Description:	This code turns the LaunchPad into a simple (slow) 
+ * 				function generator that outputs a sine wave at 128Hz.
+ * 				For each point in a period signal, there is one 
+ * 				smaller PWM period. For this example there are 32
+ * 				points per period. The duty cycle of each PWM period
+ * 				determines the analog value at that point in time.
+ * 				By continually changing the duty cycle, an analog
+ * 				signal can be generated by filtering the digital
+ * 				output signal. The analog filter can be as simple as
+ * 				a single order low-pass filter which has a corner
+ * 				frequency slightly greater than the desired signal.
+ *
+ * 				This code was originally created for "NJC's MSP430
+ * 				LaunchPad Blog".
+ * 
+ * 				See http://msp430launchpad.com for more information.
+ * 
+ * 
+ *				ACLK = n/a, MCLK = SMCLK = default DCO
+ * 
+ * 				Output Frequency = SMCLK/( # of points * PWM period)
+ * 				~128Hz = (1.0MHz to 1.1MHz)/(32*256)
+ * 
+ *               MSP430G2231
+ *             ---------------
+ *         /|\|               |
+ *          | |           P1.0| --> Analog Filters --> ~128Hz Sine Wave
+ *          --|RST            |
+ *            |               |
+ *
+ * 
+ * Author:	Nicholas J. Conn - http://msp430launchpad.com
+ * Email:	webmaster at msp430launchpad.com
+ * Date:	06-05-11
+ *
+ ************************************************************************/
+
+#include <msp430g2231.h>
+
+unsigned char counter;				// Current location in wave array
+unsigned char wave[32] = {			// Wave array, preset to values of sine
+	128, 140, 152, 164, 173, 181, 187, 191,
+	192, 191, 187, 181, 173, 164, 152, 140,
+	128, 116, 104, 92, 83, 75, 69, 65,
+	64, 65, 69, 75, 83, 92, 104, 116 };
+
+unsigned int i;						// Used for 'for' loops.
+
+void main(void)
+{
+	WDTCTL = WDTPW + WDTHOLD;					// Stop WDT
+
+	P1DIR |= BIT0;								// P1.0 output
+	counter = 0;								// Reset counter
+
+	// Initialize Timer
+	CCTL0 = CCIE;								// CCR0 interrupt enabled
+	CCTL1 = CCIE;								// CCR1 interrupt enabled
+	CCR0 = 256;									// Set PWM period to 256 clock ticks
+	CCR1 = wave[counter];						// Set first duty cycle value
+	TACTL = TASSEL_2 + MC_1 + TAIE + TACLR;		// SMCLK, upmode, enable interrupt, clear TA1R
+
+	_BIS_SR(LPM0_bits + GIE);					// Enter LPM0 w/ interrupt
+}
+
+/**
+ * TimerA0 interrupt service routine
+ **/
+#pragma vector=TIMERA0_VECTOR
+__interrupt void TIMERA0_ISR(void)
+{
+	P1OUT |= BIT0;				// Set P1.0
+
+	CCR1 = wave[counter];		// Set next duty cycle value
+	counter += 1;				// Add Offset to CCR0
+	if ( counter == 32)			// If counter is at the end of the array
+	{
+		counter = 0;			// Reset counter
+	}
+}
+
+/**
+ * TimerA1 Interrupt Vector (TAIV) handler
+ **/
+#pragma vector=TIMERA1_VECTOR
+__interrupt void TIMERA1_ISR(void)
+{
+	switch( TAIV )
+	{
+		case  2:				// CCR1 interrupt
+			P1OUT &= ~BIT0;		// Clear P1.0 to determine duty cycle.
+			break;
+		default:
+			break;
+	}
+}