The code I gave you is very crude.  It uses a loop that executes 10 NOPs=20
100 times to delay 1000 instruction cycles, but there are a lot of=20
cycles besides the NOPs that get executed, incrementing variables and=20
checking results, etc.  It wasn't intended to be accurate, just a way to=20
see if the clock was even close.

Try setting the configuration to HS or XT, with debugger off and see if=20
that helps.  If not, you may have a bad crystal.

Kerry


geetansh wrote:
> hey kerry i used your code and found some weird results
> here i used both (ur code for delay and delay_ms(10)) n the result was 10=
ms
> delay loop gave a delay of approx. 6 seconds while delay_ms gave a delay =
of
> 2 seconds and after that i changed the clock freq in code to 20MHz(using
> same 4MHz crystal) and here both delays gave a delay of 10seconds.
> i think the crystal oscillator is definitely not giving 4MHz but why dela=
y
> loop and delay function are not giving same results?
>
> code used=20
> #include <16F877A.h>
> #use delay(clock=3D20000000)
> void main()
>
> {
> int16 i,j;
> while(1)
> {
> output_D(255);
>    for(i=3D0;i<10;i++)                                //gave a delay 6sec
>    {
>       for(j=3D0;j<100;j++)                      =20
>       {
>          #asm
>             nop
>             nop
>             nop
>             nop
>             nop
>             nop
>             nop
>             nop
>             nop
>             nop
>       #endasm
>       }
> };
> output_D(0);
> delay_ms(10);                 // gave a delay of 2sec.
> }
> }
>
>
>
> Kerry Wentworth wrote:
>  =20
>> My somewhat outdated CCS compiler does delays using NOPs in a loop, not=
=20
>> a timer.  Also, the 877 has no internal oscillators.
>>
>> Since you don't enable interrupts (and they default to 'off'), it seems=
=20
>> to me it can only be 2 things:
>>
>> 1)  The debugger is using a LOT of time (seems unlikely)
>>
>> 2)  The oscillator is not really running at 4MHz.
>>
>> Try running without the debugger (config=3D0F09), because that's easy.
>> If that doesn't do it, write your own delay
>>
>> ms_delay(int d)  // Only works with 4MHz clock!!!
>> {
>>     for(i=3D0;i<d;i++)
>>     {
>>        for(j=3D0;j<100;j++)
>>        {
>>           #asm
>>              nop
>>              nop
>>              nop
>>              nop
>>              nop
>>              nop
>>              nop
>>              nop
>>              nop
>>              nop
>>        #endasm
>>        }
>>     }
>> }
>>
>> If that gives you the correct delay, the problem is the delay_ms()=20
>> routine, otherwise, it is the clock frequency.
>>
>> Kerry
>>
>> geetansh arora wrote:
>>    =20
>>> sorry i missed some details which might be important in solving this
>>> problem.
>>>
>>> I started with my first project but it didn't worked so i decided to go
>>> back
>>> and blink leds,now the problem is when the delay between on off  was se=
t
>>> 10ms the leds took 2.3sec(used a stopwatch n delay was approx. 2.3sec).
>>> At first delay was set to 500ms but it took too much time to blink so
>>> delay
>>> was set to 10ms.
>>> CCS compiler demo version was used for compiling , 4MHz crystal
>>> oscillator
>>> was used with 22pF capacitors and configuration bits 2F09 were entered =
in
>>> PICKIT 2 v2.61 (not used in the code)
>>>
>>> #include <16F877A.h>
>>> #use delay(clock=3D4000000)
>>> void main()
>>> {
>>> while(1)
>>> {
>>> output_D(255);
>>> delay_ms(10);
>>> output_D(0);
>>> delay_ms(10);
>>> }
>>> }
>>> please solve my problem guys.
>>> thank you and sorry again for missing the details in previous post.
>>> =20

--=20
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