On Sun, 17 Mar 2002, Dale Botkin wrote:

> On Sun, 17 Mar 2002, Lasse Madsen wrote:
>
> > I was wondering if its possible to make 2 oscillators running in one
> > pic at the same time ? the PIC is a 12C50x with external 4MHz crystal
> > and oscillators should be on 100KHz and 50Hz.
>
> Tall order, you're talking about switching the output pin every 5
> instruction cycles for the 100KHz output.  That's simple as long as you
> don't need to do anything else!

I saw Olin's post, but the original question was to generate two
frequencies simultaneously.



100000/50/2 = 2000

     movlw  low(2000/2) + 1      ;+1 because Z instead of C
     movwf  lo_50hz              ;is used to monitor roll over
     movlw  high(2000/2) + 1     ; the /2 is because two cycles
     movwf  hi_50hz              ;of the 100k wave are generated
                                 through each pass in the loop
     movf   ioport,w

loop
     movwf  ioport               ;0
     iorlw  (1<<iobit_100k)      ;1
     decf   lo_50hz,f            ;2 Note that the high byte is decremented
     skpnz                       ;  when the low byte reaches zero and not
     decf   hi_50hz,f            ;4 when it rolls over to 0xff. A trick...

     movwf  ioport               ;5

     skpz                        ;6 Z will be set if 50Hz counter is at
      goto  roll_over50hz        ;7 the end.
     andlw  ~(1<<iobit_100k)     ;8

     nop                         ;9 - whew  - a free cycle!

     movwf  ioport               ;10

     iorlw  (1<<iobit_100k)      ;11
     nop
     goto   $+1

     movwf  ioport               ;15
     andlw  ~(1<<iobit_100k)     ;16

     nop                         ;17
     goto   loop                 ;18,19


roll_over50hz:

     xorlw  (1<<iobit_50hz)      ;9
     movwf  ioport               ;10

     movlw  low(2000/2) + 1      ;+1 because Z instead of C
     movwf  lo_50hz              ;is used to monitor roll over

     movf   ioport,w
     andlw  ~(1<<iobit_100k)
     movwf  ioport

     movlw  high(2000/2) + 1
     movwf  hi_50hz

     movf   ioport,w
     iorlw  (1<<iobit_100k)
     movwf  ioport
     nop
     nop
     andlw  ~(1<<iobit_100k)
     goto   loop


This is of course untested.

Scott

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