Hi,

Firstly, thanks to all who replied to my previous problem concerning
concurrency on the 84.

I wish to implement a 16 bit timer on a PIC 84. I'm using a 32KHz
XTAL and plan to set the prescaler so that the 8 bit PIC timer
overflows every 500mS.

The period of the events I need to measure can be up to 3 seconds. I
cannot increase the prescaler value as I need the 1/512 S resoultion.

Also I cannot do not want to use the timer overflow interrupt unless
absolutely necessary. Therefore I initially proposed the following;


BEGIN
. WHILE forever
. . IF the timer overflow flag is set
. . . Increment Period_Hi
. . IF the event has occurred
. . . Copy the timer contents to Period_Lo
. . . IF the timer overflow flag is set
. . . . Increment Period_Hi
. . . ENDIF
. . . Process the event Period
. . ENDIF
. ENDWHILE
END

As can be seen a problem can occur when a timer overflow occurs
between checking the overflow bit and reading the timer contents.
Even if the overflow check is done immediately befor or after
reading the timer contents, the broblem will still exist.

Is there a standard way for handling this problem, as it must be
fairly common.

I look forward to your input.


 Peter.
--
_______________________________________________________________________
Peter Homann   email: peterh@adacel.com.au       Work : +61 3 9596-2991
Adacel Pty Ltd                                   Fax  : +61 3 9596-2960
250 Bay St, Brighton 3186, VIC, AUSTRALIA      Mobile :     014 025-925