Hi,

the time you said makes me suspect that is is the Watchdog Reset. To
locate the nature of this phenomena I suggest to check the PD and TO bits
immediately after sleep.

Imre


On Mon, 14 Sep 1998, Tom Crane wrote:

> Dear All,
>         I am not getting the sort of timing on wakeup from the SLEEP
> instruction on a PIC16C84 based system I'm working on that I had (naively?)
> expected. The datasheet (DS30081F) is not explicit on this point I would be
> interested if anybody could confirm/refute my findings.
>
> I am clocking the chip at 4MHz and am executing some test code,
>
>  < Clear all bits in INTCON - ie. ensure GIE=0>
>  < Zero PORT registers & Turn PORT A & B to Inputs>
>  bsf     STATUS, RP0     ; Select Register Bank 1
>  bsf     OPTION_REG, INTEDG; Choose Int Interrupt on RB0 rising edge transitio
n
>  bcf     STATUS, RP0     ; Reselect Register Bank 0
>  bsf     INTCON, INTE    ; Enable Int interrupt
>  bcf     INTCON, INTF    ; Clear Int Flag first
>  sleep                   ; Execute the SLEEP instruction
>  movf    PORTB, W        ; PIC has woken up, So read PORTB to clear its port c
hange mismatch condition
>  bcf     INTCON, INTF    ; Clear the INTF flag which signalled the Int Interru
pt condition
>  < Zero PORT registers & Turn PORT A & B to Outputs>
>  bsf     PORTB, 7
>  bcf     PORTB, 7
>  <etc.>
>
> When using an internal clock (ie. 4MHz crystal + usual 2 caps) I find that the
> delay between applying a rising-edge signal to RB0 and detecting the signal on
> RB7 is ~10mS, varying several mS from occasion to occasion.
>
> When feeding the PIC with an external 4MHz clock the delay is ~200mS.
>
> Presumably dependence on clock source is due to the 'oscillator driver' needin
g
> to restart when running on internal clock - the datasheet describes it as bein
g
> turned off in sleep mode.
>
> In any event, since my application needs to wake the PIC with a precision of 1
> machine cycle - ie. 1uS w.r.t. the applied interrupt RB0 signal, I assume I'm
> wasting my time messing about with the SLEEP instruction ?...
>
> Regards.
> Tom.
> --
> Tom Crane, Dept. Physics, Royal Holloway, University of London, Egham Hill,
> Egham, Surrey, TW20 0EX, England.
> Email:  uhap023@vms.rhbnc.ac.uk
> SPAN:   19.875
> Fax:    01784 472794
>
>