PIC18F8720 Analog Comparator

[demarware]

Hello,

I'm trying implement a comparator interrupt; based on the example EX_COMP.C. (and searching this board)

I'm using an external ref. (200mV, <10K Z), and an input of 0-4V.

Here's the code
#include <18F8720.h>
#device *=16
#device icd=true

#fuses HS, BROWNOUT, NOWDT, PUT, DEBUG, NOLVP
#use delay(clock=19660800)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, ERRORS)

short safe_conditions=TRUE;

#INT_COMP
void isr() {

safe_conditions=FALSE;
printf("WARNING!! Voltage level is above ref. \r\n");
}


main() {

printf("\r\nRunning voltage test...\r\n\n");

//setup_comparator(A1_VR_OUT_ON_A2);
//setup_vref(VREF_HIGH|15);

setup_comparator(F6_F5_NC_NC_OUT_ON_F2);

enable_interrupts(INT_COMP);
enable_interrupts(GLOBAL);

while(TRUE)
{
if(safe_conditions)
printf("Voltage level is below ref. \r\n");
safe_conditions=TRUE;
delay_ms(500);
}
}
]

This works as expected, however I need an interrupt when the input is below the ref. So I thought I would only need to switch the inputs?? But that doesn't work, I get the same results.

Except if I debug/break, then switch the wires, then resume execution - I get the irq when the input is < ref. Restarting from a reset produces the opposite.

Where am I confused?

And, the datasheet says "The comparator interrupt flag is set whenever there is a change in the output value of either comparator." This code seems to produce an interrupt whenever X>Y only (even if it is always >), and not on the change back to X<Y. Is that due to the ccs implementation?

Oh yeh, v3.191. (this is the version I should be using right?)

Thanks in advance.
[/code]

[PCM programmer]

Both the data sheet and the reference manual state that you must
clear the "change condition" by reading (or writing) the CMCON register.
So I think you should add the lines shown below in bold:

#byte CMCON = 0xFB4

#INT_COMP
void isr() {
char c;
c = CMCON;
safe_conditions=FALSE;
printf("WARNING!! Voltage level is above ref. \r\n");
}

PIC18 reference manual for the comparator module:
http://ww1.microchip.com/downloads/en/DeviceDoc/39524.pdf

[demarware]

Thanks, Now I have both changes.

[demarware]

FYI

use bit_test () on CMCON to detect change "direction".

#int_COMP
COMP_isr()
{

byte b;
b = CMCON;

if(bit_test (b, 6)) //c1out
{

//
}
else
{

//
}

}