Spehro Pefhany wrote:
> At 06:49 AM 5/27/2005 -0700, you wrote:
> 
> 
>>  A 20MHz clocked PIC would update the PWM counters every 50 cycles
>> * 0.2uS/cycle = 25 uS. The PWM period is 256 * 25uS ~ 6.4mS which
>> translates into a PWM frequency of 1/6.4mS = 156Hz. Triggering the LED
>> refresh at this frequency should be fast enough to remove perceivable
>> flicker.
> 
> 
> Scott, 156Hz is nowhere near fast enough in most cases.
<snip>

Sure. Whatever...

What I find incredulous is that many people are stating very obvious 
facts but the original poster is having trouble grokking it. What he 
should've of said is, " I saw this routine for PWM'ing 8 I/O pins and 
since I'm using the 18F452 I figured out how to save 9-bytes of RAM. For 
example, you can replace the DECFSZ with a CPFSEQ in the pwm_update 
section and write:

pwm_update:
         MOVF    rising_edge,W
         CLRF    temp

         CPFSEQ  pwm0,F          ;If the first pwm has not reached the
          BSF    temp,0          ;end then don't turn it off.
                                 ;
         CPFSEQ  pwm1,F          ;Same for the second one
          BSF    temp,1          ;
                                 ;
         CPFSEQ  pwm2,F          ;
          BSF    temp,2          ;
                                 ;
    ....

         MOVF    temp,W
         ANDWF   PWM_LATCH

         RETURN

The 8-bytes for the counters in the old routine are no longer needed. 
The 9'th byte saved is 'pwm_state'. Now we can use I/O port's latch."

But we didn't see that.

Scott
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist