16/5/2000

        First question is what is the accuracy of your resonator? You have
imposed a requirement of 400ppm.
All that aside at the frequency your are running at  the time that it takes
to call the function is a very small percentage of the error.
Can you give us more of an explanation, what is the error  that you are
observing etc


Dennis



> -----Original Message-----
> From: Samuel Ace Winchenbach [SMTP:swinchen@EECE.MAINE.EDU]
> Sent: Tuesday, 16 May 2000 9:44
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      Helping someone new to this...
>
> Hello all.
>
> I am working on a small robot project and need to generate a pulse at 40 -
> 60 hz (from what I have read so far on servos) that is accurate to within
> .01 ms.  I will be using a 16F84 and a 10.0 MHz ceramic resonator.  I have
> done the following math...
>
> 10000000 cycle/sec * 1 instruction/4 cycles = 2500000 instructions/sec.
>
> now assuming that I do not prescale it...  I also have 2500000 TMR0
> Increases/sec.
>
> 2500000 TMR0 Increases/sec * 1 loop/X TMR0 Increases = 1000 loops/sec
>
> X = 2500 TMR0 Increases = 10 * 250 TMR0 increases
>
> with this in mind I wrote a simple function in PIC C (I do not
> assembler...
> I really wish I did)
>
> void delay(long int times, int cycles)
> {
>         long int i;
>         for(i = 0;i < times;i++)
>         {
>                 TMR0 = 0;
>                 while(TMR0 < cycles);
>         }
> }
>
> so to use this function I should call it like this:
>
> while(1)
> {
>   servo = 1 //turn the servo bit on
>   delay(10,250); //delay for 1 ms.
>   servo = 0;  //turn the servo bit off.
>   delay(xxx,xxx);  //where xxx,xxx is the numbers needed for a 40hz pulse)
> }
>
> unfortunately there is a abit of error somewhere in my method, can anyone
> help me track it down?  I believe it has to do with the fact that I am not
> incorperating the amout of time it takes to execute the instructions in
> calling the "delay" routine, and each instruction within that routine.
> any
> help would be much appreciated as would any comments on the method I am
> choosing to do this.   Also could anyone recommend any good PIC books to
> help a begginer get started with PIC Assembler?
>
> Thanks,
>
> Sam