PIC 12F675 Comparator, Few Questions .

[aljamri]

Hi,

I'm doing 12F675 from this link:

Using the built in 12F675 Comparator.

Following, is the code:

// Definitions
#define COMPARATOR_OP 2
#define LED 4

///////////////////////////////////////////////////////
void init_ports(void) {
   //GP0 & GP1 are inputs
   TRISIO = 0 | (1<<GP0) | (1<<GP1); // 0 - op, 1 - ip

   ANSEL = (1<<GP0) | (1<<GP1); ; // Ana. ip on GP0 GP1
}

///////////////////////////////////////////////////////
void init_comparator(void) {
   // Comparator with external input and output.
   // Cout = 0 (comparator output), Cinv =0 (inversion)

   [COLOR="#ff0000"][B]CMCON = 0x01;[/B][/COLOR]

}

///////////////////////////////////////////////////////
// Start here
void main() {
int i;

   init_ports();

   // Show device is active on power up.
   for (i=0;i<5;i++) {

      GPIO |= (1<<COMPARATOR_OP);
      delay_ms(100);

      GPIO &= ~(1<<COMPARATOR_OP);
      delay_ms(100);
   }

   init_comparator();

   while(1) {;
      GPIO |= (1<<LED);
      delay_ms(100);

      GPIO &= ~(1<<LED);
      delay_ms(100);
   }
}

The code works fine using the provided circuit. Then I've replaced the comparator Potentiometer VR1 with a 10k resistor in series with LDR. The circuit still works fine, The output LED D1 stays OFF, and when LDR covered, It turns ON.

I have few questions regarding the comparator and the code and here is the first:

Trying to measure my understanding, I've tried to reverse the D1 ON/OFF status by , changing CMCON command from 0x01 to ox81 ( changed Bit6 COUT from 0 to 1 ).

When programmed the PIC, the operation does not changed. What do you think is wrong?

 

[nickelflippr]

You have bit7 turned on not bit6

 

[aljamri]

Ohhhh, You are right, I've put 9 digits instead of 8. Tomorrow I'll check it and let you know. Then I'll go to the next Question.
Thanks

 

[aljamri]

Bit4 CINV is the output Inversion bit

1 = Output inverted, so CMCON = 0x11 will make my LED ON in dark and OFF in light ( using LDR )

this operation is confirmed.

 

[aljamri]

My 2nd Question is :

How to utilize the comparator action in my program. Instead of a stable 1 at output, I need to output a square wave to drive a buzzer using any other unused pin. So that I've added the following 2 lines:

switch (GPIO.F2) {
      case (0) : GPIO.F3=0;
      case (1) : GPIO.F3=1; delay_ms(500); GPIO.F3=0; delay_ms(500);
                  }

but got no output on GP3 regardless the comparator condition. Is there another idea ?

 

[nickelflippr]

O.K. second chance at it, GP3 (MCLR) is input only pin, try GP5. Or use GP2 by setting up the CMCON register for no output.

 

[be80be]

GPO3 is input only

CLRF GPIO ;Init GPIO
MOVLW 07h ;Set GP<2:0> to
MOVWF CMCON ;digital IO
BSF STATUS,RP0 ;Bank 1
CLRF ANSEL ;Digital I/O

 

[aljamri]

Yes, I've used GP5 as output and got everything working fine. My buzzer is sounding whenever it is dark. My next step is to immigrate the same program into a larger PIC such as 16F6XX and 16F7XX and try to test all their comparators and let you know my progress.

Thanks for all.

 

[be80be]

It's a will be easy to reuse your code with 16f6xx chips just a little name changes and you'll be good to go

 

[aljamri]

Tried to get it work on PIC16F628A but no chance. Here is the code:

void init_ports(void) {

   TRISA = 0x0F; // RA.0:RA.3 INPUTS
                 // RA.4:RA.7 OUTPUTS
}

void init_comparator(void) {
   // Both Comparators with external input and output.

   CMCON = 0x04;
}

// Start here
void main() {
int i;
//
   init_ports();
//
//   // Show device is active on power up.
   for (i=0;i<5;i++) {

      PORTA.F2 = 1;
      delay_ms(100);

      PORTA.F2 = 0;
      delay_ms(100);
   }


   init_comparator();

   while(1) {;
   
      PORTA.F6=1;delay_ms(500);PORTA.F6=0; delay_ms(500);

                           }
}

The last part of the code is working fine, the LED conncted to PortA.F6 is flashing, but Comparator 2 output at RA4 shows no difference regard less the change in its inputs, RA1 (adjustable) and RA2 2.5V via 10K resistor as a reference.