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Using the MSP-EXP430FG4618 Development Tool analyse the Comparator_A operation. A voltage is applied to one of the Comparator’s inputs, generated optionally by the DAC12 or by other external source. Whenever the external voltage value is higher than the comparison value internally generated, it is generated an interrupt that switches the LED state.

Laboratory signal acquisition: lab4 - voltage signal comparison with comparator_a


This laboratory gives examples of the uses of the ADC types available in the hardware development kits. A different laboratory is developed for each kit, taking into account that both the ADC10 and the SD16_A laboratories implement a temperature data logger. The ADC12 laboratory also uses operational amplifiers to perform the analogue signal conditioning.


This laboratory ( Lab4_ADC.c ) analyses Comparator_A operation. A voltage is applied to one of the Comparator’s inputs, generated either by the DAC12 or by other external source. Whenever the external voltage value is higher than the comparison value internally generated, an interrupt is generated that switches the LED state.


The resources used by the application are:

- DAC12;

- Comparator_A;

- Digital IO;

- Timer_A.

Software application organization

The application starts by stopping the Watchdog Timer.

Timer_A is configured to generate an interrupt once every msec, and updates the DAC12 output in order to provide a ramp signal.

The Comparator_A’s output is configured to be accessible at pin P6.6, which is available on Header 4 pin 7. The signal applied to CA0 input is compared with 0.5 V cc internal reference voltage. Every time that a compare match occurs, an interrupt is requested and switches the state of LED1.

System configuration

Comparator_a configuration

Configure the registers in order to receive the external signal at the CA0 input and compare it with the internal reference 0.5 V cc . Enable the comparator with an interrupt triggered on a low-to-high transition of the comparator output.

CACTL1 = CAON | CAREF_2 | CARSEL | CAIE; // Enable comp, ref = 0.5*Vcc CACTL2 = P2CA0; // Pin to CA0P2DIR |= 0x042; // P2.1 and P2.6 output direction P2SEL |= 0x040; // P2.1 = LED1 and P2.6 = CAOUTCACTL1 |= CAIE; // Setup interrupt for Comparator //*********************************************************// Comp_A interrupt service routine -- toggles LED //*********************************************************#pragma vector=COMPARATORA_VECTOR __interrupt void Comp_A_ISR (void){ CACTL1 ^= CAIES; // Toggles interrupt edgeP2OUT ^= 0x02; // Toggle P2.1 }

Adc12 configuration

ADC12CTL0 = REF2_5V + REFON; // Internal 2.5V ref on

Dac12 configuration

DAC12_0DAT = 0x00; // DAC_0 output 0V

DAC12_0CTL = DAC12IR | DAC12AMP_5 | DAC12ENC; // DAC_0->P6.6 // DAC reference Vref// 12 bits resolution // Imediate load// DAC full scale output // Medium speed/current// Straight binary // Not grouped

Timer_a configuration

// Compare mode TAR = 0; // TAR resetTACCR0 = 13600; // Delay to allow Ref to settle TACCTL0 |= CCIE; // Compare-mode interruptTACTL = TACLR + MC_1 + TASSEL_2; // up mode, SMCLK // Interrupt enableTAR = 0; // TAR reset TACCTL0 = CCIE; // CCR0 interrupt enabledTACCR0 = 32; // 1 msec counting period TACTL = TASSEL_1 | MC_1 | ID_0; // ACLK, up mode//********************************************************* // ISR to TACCRO from Timer A//********************************************************* #pragma vector=TIMERA0_VECTOR__interrupt void TimerA0_ISR (void) {DAC12_0DAT++; if (DAC12_0DAT == 0xFFF) DAC12_0DAT = 0;if (flag == 1) // if flag active exit LPM0{ flag = 0;LPM0_EXIT; }}

Analysis of operation

The experimental verification of this laboratory can be accomplished by connecting the DAC12’s output, available on Header 8 pin 7, to the Comparator_A’s input CA0, available on Header 4 pin 7.

Observe the signals wave form at the Comparator_A’s input and output using an oscilloscope. The LED1 switches state whenever the input’s voltage value is lower than the compare value.

This example and many others are available on the MSP430 Teaching ROM.

Request this ROM, and our other Teaching Materials here (External Link)

Questions & Answers

what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
how nano science is used for hydrophobicity
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
what is differents between GO and RGO?
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
How can I make nanorobot?
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
how can I make nanorobot?
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
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Source:  OpenStax, Teaching and classroom laboratories based on the “ez430” and "experimenter's board" msp430 microcontroller platforms and code composer essentials. OpenStax CNX. May 19, 2009 Download for free at http://cnx.org/content/col10706/1.3
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