comparator

[ElectroNick]

Hi,

i want to use pic16f785's comparator module. VCC is 4.88V and I want comparator to control a led. But i can't success! The voltage on RA1 is about 4.7V but led is still passive. Could you please help me?

Here is my code:

[foothill]

Nick,

The code in main will run one pass, then stop if
the isr is not called. And If there are any problems in your isr,
the code will stall.

What's needed for troubleshooting is an infinite loop to
force main() to repeat endlessly. Try:

includes
.
variable declarations
.
comparator setups
.
main()

while (TRUE)
{

---Your main code body here----

}

Also, I often toggle an otherwise unused pin directly
somewhere in main, so I can see if main is running.
You can do the same in your isr, just to see if it's being
called. Try to get the whole structure running in some very
simple way, then add in the comparator function and isr.

Be aware that explicit function calls cannot be made from
within another function....they can't be nested. I always
put conditional comparator setup changes in the body of
main rather than in an isr, and if they're not to change, I
put them above main altogether...

Check the sample comparator program sent with the
compiler. Samples often give good tips.

Good luck!

Brian

[Ttelmah]

Ongoing to the above comment, _do not_ disable and enable the global interrupt in the interrupt handler. Doing this is a way to crash the PIC if the interrupt occurs a second time quickly. The interrupts are automatically disabled by the hardware, when an interrupt occurs, and automatically re-enabled when you return from an interrupt. If you re-enable before the return, and another interrupt is pending, the chip will interrupt inside the interrupt handler, and this results in a 'recursive' call, which the chip does not support.
You also don't need to re-enable the int_comp in the handler. It does not get disabled, and this is just uneccessary.

Best Wishes