Doug R. Boulware <dougrb@SQUEAKY.FREE.ORG> wrote:
>
>The Parallax simulator shows that a PIC16C84 will awaken from sleep by
>an RTCC overflow interrupt that is triggered from the RA4/RTCC input
>pin.
>
>I have not found any documentation that confirms this, and cannot seem
>to get it to occur on the actual chip.  I am attempting to awaken the
>chip when a start bit from an RS232 serial input is detected.  The
>serial input routine is interrupt driven from the RTCC and works fine
>without the sleep instruction.
>
>Can this be done ?

Doug:

Sure, but contrary to what that substandard simulator shows, it can't
be done with only the RTCC pin.  Check out section 8.8.1, "Wake-Up from
Sleep", in the 16C84 Data Sheet; the only events which can wake up the
PIC are:

    External reset input on MCLR
    WDT timeout reset
    Interrupt from RB0/INT, PortB-change, or data EEPROM write-complete

Yuo might also want to take a look at Section 6.1, "TIMER0 (TMR0)
INTERRUPT", which says, in so many words, "The TMR0 module interrupt
cannot wake the processor from SLEEP...."

If your RB0 pin is available, I'd tie it to the RA4/RTCC pin and
configure the RB0 interrupt to occur when it sees the start bit.

That'll wake up the PIC; once awake, you can disable the RB0 interrupt
during the reception (so you don't get repeated RB0 interrupts), then
re-enable it just before you go to sleep.

-Andy

--
Andrew Warren - fastfwd@ix.netcom.com
Fast Forward Engineering, Vista, California