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ADC12CTL0 = REF2_5V | REFON; // Internal 2.5V ref on
The DAC12_0 is configured with 12-bit resolution. The output is updated immediately when a new DAC12 data value is written in straight binary data format to the DAC12_0DAT register.
The full-scale output must be equal to the V REF+ 2.5 V internal reference voltage. Choose a compromise solution between the settling time and current consumption, by selecting a medium frequency and current for both input and output buffers. Configure the following register in order to meet these specifications:
DAC12_0DAT = 0x00; // DAC_0 output 0VDAC12_0CTL = DAC12IR | DAC12AMP_5 | DAC12ENC;
// DAC_0 ->P6.6,
// DAC_1 ->P6.7,
// DAC reference Vref,// 12 bits resolution,
// Immediate load,// DAC full scale output,
// Medium speed/current,// Straight binary,
// Not grouped
Configure Timer_A register to enable an interrupt once every 1 msec. Use the ACLK clock signal as the clock source. This timer is configured in count up mode in order to count until the TAR value reaches the TACCR0 value.
// Before entering in LPM0:
TACTL = TACLR | MC_1 | TASSEL_2; // up mode, SMCLK// Timer_A ISR:TAR = 0; // TAR reset
TACCR0 = 13600; // Delay to allow Ref to settleTACCTL0 |= CCIE; // Compare-mode interrupt
TACTL = TACLR | MC_1 | TASSEL_2; // up mode, SMCLK//*********************************************************// ISR to TACCRO from Timer A
//*********************************************************#pragma vector=TIMERA0_VECTOR
__interrupt void TimerA0_ISR (void){
DAC12_0DAT++; // Increase DAC's outputif (DAC12_0DAT == 0xfff)
DAC12_0DAT = 0; // reset DAC's outputif (flag == 1) // if flag active exite LPM0
{flag = 0;
LPM0_EXIT;}
}
Port P1 uses the bits P1.0 and P1.2 to activate the ISR whenever the push buttons SW1 and SW2 are activated (low-to-high transition).
// SW1 and SW2 ports configuration
P1SEL&= ~0x03; // P1.0 and P1.1 I/O ports
P1DIR&= ~0x03; // P1.0 and P1.1 digital inputs
P1IFG = 0x00; // clear all interrupts pendingP1IE |= 0x03; // enable port interrupts
DAC12_0 is connected to P6.6. Configure P6 as a special function output:
// P6.6 (DAC12_0 output)
// There is no need to configure P6.6 as a// special function output since it was configured in the
// DAC12 configuration register (DAC12_0CTL) using// DAC12OPS = 0//*********************************************************
// Port1 Interrupt Service Rotine//*********************************************************
#pragma vector=PORT1_VECTOR__interrupt void PORT1_ISR (void)
{if (P1IFG&0x01) // SW1 generate interrupt
DAC12_0DAT += 400; // DAC's output increases
if (P1IFG&0x02) // SW2 generate interrupt
DAC12_0DAT -= 400; // DAC's output decreases
P1IFG = 0x00; // clean all pending interrupts
}
After compiling the project and starting the debug session, monitor the operation of the application using an oscilloscope probe connected to pin 7 of Header 8 (P6.6).
Assign different values to the bits set in DAC12AMP0. Suspend the execution of the application then directly change the registers. Do not forget that this change requires suspending the operation of the DAC12 by disabling the bit DAC12ENC. Afterwards, this bit must be enabled.
Please note the special cases relating to:
- DAC12 off;
- High impedance output and DAC12 off;
- Output: 0 V.
This example and many others are available on the MSP430 Teaching ROM.
Request this ROM, and our other Teaching Materials here (External Link)
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