MSP430 Comparator

I have studied the 430 comparator these two days. At the beginning, I didn't understand what it was. I read the blogs on this website and seemed to understand it, but when it came to programming, I had no idea where to start. However, God will not let those who work hard, and I finally understood it.

In fact, here you just need to understand a picture, two registers, and understand the working principle.

This is the logic diagram of comparator A. Comparator A consists of 4 parts.

Label 1: Internal reference voltage generator, which can generate reference voltage of 0.25V, 0.50v

Label 2: External voltage input terminal, CA0 corresponds to P2.3, CA1 corresponds to P2.4

Label 3: Internal comparator. I just learned about comparators in class today. That is, when the positive input is greater than the negative input, the comparator outputs a 1 and generates an interrupt flag.

Label 4: comparison result input terminal

Therefore, the general template can be produced

1: Set the internal reference voltage

2: Open the external input port

3: Set the properties of external I/O, that is, the input properties of P2.3 or P2.4

4: Determine the output result

Step 1 corresponds to step 1 in the previous step: At this time, you need to be familiar with the registers. Comparator A has two registers CACTL1 and CACTL2

CACTL1 is used to set the internal reference voltage: Here is a template example: CACTL1 = CARSEL+CAREF1+CAON;

Translation is, set CACTL1 = internal reference voltage to the positive or negative input of the comparator + select 0.25V reference voltage or 0.5V reference voltage + turn on comparator A

Step 2 corresponds to 2 in the previous step

Open the external input port: use CACTL2, CACTL2=P2CAO

The translation is that the external selection is P2CAO, which means P2.3 is used as the input terminal.

Step 3: Set I/O properties

P2DIR = 0x00; //Set IO as the input of the comparator
 P2SEL |= BIT3;

Step 4: Compare input and output results:

At this time, you should also be familiar with the register. The lowest bit in CACTL2, that is, CAOUT, if the positive end is greater than the negative end, cout becomes 1. At this time, the typical judgment statement is

if((CACTL2|0xfe) == 0xff) //If the lowest bit is set to 1, the lowest bit in CACTL1, that is, the interrupt flag of the comparator, will also be set

{

      Further operation;

      The interrupt flag is set to 1

}

Sample code: Compare the voltage of P2.3 input with 0.25. If it is greater, light up the LED and clear the interrupt flag.

#include

void main( void )

{

  // Stop watchdog timer to prevent time out reset

  WDTCTL = WDTPW + WDTHOLD;

  CACTL1 =CARSEL +CAREF1 +CAON;

  CACTL2 = P2CA0;

  P2DIR = 0x00; //Set IO as the input of the comparator

  P2SEL |= BIT3;

  P3OUT |= BIT5;

  P3DIR |= BIT5;

  while(1)

  {

      if((CACTL2 | 0xfe) == 0xff)

      {

        P3OUT &=~BIT5; //Compare if the voltage exceeds 0.25V

        CACTL1 &=0xfe; //Clear interrupt flag

      }

      else

      {

         P3OUT |= BIT5;

      }

  }

}