Other Parts Discussed in Thread: MSP-EXP430FR5969
Hi there,
I am very new to the MSP430 and I am a bit confused by how the 12-bit ADC works. I have an MPC9700 thermistor hooked up to my MSP-EXP430FR5969 Launchpad and I am using the following code example to test it:
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//******************************************************************************
// MSP430FR59xx Demo - ADC12, Sample A1, 1.2V Shared Ref, Set P1.0 if A1 > 0.5V
//
// Description: A single sample is made on A1 with reference to internal
// 1.2V Vref. Software sets ADC12SC to start sample and conversion - ADC10SC
// automatically cleared at EOC. ADC12 internal oscillator times sample (16x)
// and conversion. In Mainloop MSP430 waits in LPM0 to save power until ADC12
// conversion complete, ADC12_ISR will force exit from LPM0 in Mainloop on
// reti. If A1 > 0.5V, P1.0 set, else reset.
//
// MSP430FR5969
// -----------------
// /|\| XIN|-
// | | |
// --|RST XOUT|-
// | |
// >---|P1.3/A1 P1.0|-->LED
//
// William Goh
// Texas Instruments Inc.
// February 2014
// Built with IAR Embedded Workbench V5.60 & Code Composer Studio V5.5
//******************************************************************************
#include <msp430.h>
int main(void)
{
WDTCTL = WDTPW | WDTHOLD; // Stop WDT
// GPIO Setup
P1OUT &= ~BIT0; // Clear LED to start
P1DIR |= BIT0; // P1.0 output
P1SEL1 |= BIT3; // Configure P1.3 for ADC
P1SEL0 |= BIT3;
// Disable the GPIO power-on default high-impedance mode to activate
// previously configured port settings
PM5CTL0 &= ~LOCKLPM5;
// By default, REFMSTR=1 => REFCTL is used to configure the internal reference
while(REFCTL0 & REFGENBUSY); // If ref generator busy, WAIT
REFCTL0 |= REFVSEL_0 | REFON; // Select internal ref = 1.2V
// Internal Reference ON
// Configure ADC12
ADC12CTL0 = ADC12SHT0_2 | ADC12ON;
ADC12CTL1 = ADC12SHP; // ADCCLK = MODOSC; sampling timer
ADC12CTL2 |= ADC12RES_2; // 12-bit conversion results
ADC12IER0 |= ADC12IE0; // Enable ADC conv complete interrupt
ADC12MCTL0 |= ADC12INCH_3 | ADC12VRSEL_3; // A1 ADC input select; Vref=1.2V
while(!(REFCTL0 & REFGENRDY)); // Wait for reference generator
// to settle
while(1)
{
__delay_cycles(5000); // Delay between conversions
ADC12CTL0 |= ADC12ENC | ADC12SC; // Sampling and conversion start
__bis_SR_register(LPM0_bits + GIE); // LPM0, ADC10_ISR will force exit
__no_operation(); // For debug only
}
}
#if defined(__TI_COMPILER_VERSION__) || defined(__IAR_SYSTEMS_ICC__)
#pragma vector = ADC12_VECTOR
__interrupt void ADC12_ISR(void)
#elif defined(__GNUC__)
void __attribute__ ((interrupt(ADC12_VECTOR))) ADC12_ISR (void)
#else
#error Compiler not supported!
#endif
{
switch (__even_in_range(ADC12IV, ADC12IV_ADC12RDYIFG))
{
case ADC12IV_NONE: break; // Vector 0: No interrupt
case ADC12IV_ADC12OVIFG: break; // Vector 2: ADC12MEMx Overflow
case ADC12IV_ADC12TOVIFG: break; // Vector 4: Conversion time overflow
case ADC12IV_ADC12HIIFG: break; // Vector 6: ADC12BHI
case ADC12IV_ADC12LOIFG: break; // Vector 8: ADC12BLO
case ADC12IV_ADC12INIFG: break; // Vector 10: ADC12BIN
case ADC12IV_ADC12IFG0: // Vector 12: ADC12MEM0 Interrupt
if (ADC12MEM0 >= 0x6B4) // ADC12MEM = A1 > 0.5V?
P1OUT |= BIT0; // P1.0 = 1
else
P1OUT &= ~BIT0; // P1.0 = 0
__bic_SR_register_on_exit(LPM0_bits); // Exit active CPU
break; // Clear CPUOFF bit from 0(SR)
case ADC12IV_ADC12IFG1: break; // Vector 14: ADC12MEM1
case ADC12IV_ADC12IFG2: break; // Vector 16: ADC12MEM2
case ADC12IV_ADC12IFG3: break; // Vector 18: ADC12MEM3
case ADC12IV_ADC12IFG4: break; // Vector 20: ADC12MEM4
case ADC12IV_ADC12IFG5: break; // Vector 22: ADC12MEM5
case ADC12IV_ADC12IFG6: break; // Vector 24: ADC12MEM6
case ADC12IV_ADC12IFG7: break; // Vector 26: ADC12MEM7
case ADC12IV_ADC12IFG8: break; // Vector 28: ADC12MEM8
case ADC12IV_ADC12IFG9: break; // Vector 30: ADC12MEM9
case ADC12IV_ADC12IFG10: break; // Vector 32: ADC12MEM10
case ADC12IV_ADC12IFG11: break; // Vector 34: ADC12MEM11
case ADC12IV_ADC12IFG12: break; // Vector 36: ADC12MEM12
case ADC12IV_ADC12IFG13: break; // Vector 38: ADC12MEM13
case ADC12IV_ADC12IFG14: break; // Vector 40: ADC12MEM14
case ADC12IV_ADC12IFG15: break; // Vector 42: ADC12MEM15
case ADC12IV_ADC12IFG16: break; // Vector 44: ADC12MEM16
case ADC12IV_ADC12IFG17: break; // Vector 46: ADC12MEM17
case ADC12IV_ADC12IFG18: break; // Vector 48: ADC12MEM18
case ADC12IV_ADC12IFG19: break; // Vector 50: ADC12MEM19
case ADC12IV_ADC12IFG20: break; // Vector 52: ADC12MEM20
case ADC12IV_ADC12IFG21: break; // Vector 54: ADC12MEM21
case ADC12IV_ADC12IFG22: break; // Vector 56: ADC12MEM22
case ADC12IV_ADC12IFG23: break; // Vector 58: ADC12MEM23
case ADC12IV_ADC12IFG24: break; // Vector 60: ADC12MEM24
case ADC12IV_ADC12IFG25: break; // Vector 62: ADC12MEM25
case ADC12IV_ADC12IFG26: break; // Vector 64: ADC12MEM26
case ADC12IV_ADC12IFG27: break; // Vector 66: ADC12MEM27
case ADC12IV_ADC12IFG28: break; // Vector 68: ADC12MEM28
case ADC12IV_ADC12IFG29: break; // Vector 70: ADC12MEM29
case ADC12IV_ADC12IFG30: break; // Vector 72: ADC12MEM30
case ADC12IV_ADC12IFG31: break; // Vector 74: ADC12MEM31
case ADC12IV_ADC12RDYIFG: break; // Vector 76: ADC12RDY
default: break;
}
}
I am receiving values in the range of ~1900-2048ish in the ADC Memory register (or, 0x76C - ~0x800). According to my thermistor datasheet, I should be expecting 500mV + 10mV per degree Celcius. I am operating this device at room temperature and I should be expecting to see results in the range of 700-750mV as a result.
Would someone be able to help me understand how the ADC is performing these conversions and arriving at these values?
Thank you in advance,
Mike
