On Tue, 11 Dec 2001, Andre Abelian wrote:

> Hi to all engineers,
>
> I need to generate 4 pulses at the same time with
> Different timing and based on battery voltage if
> The voltage does lower then +12 v duty cycle (on time)
> Must be changed go lower then 50%.
>
>
>
>               |--------------------|                    |------
> ______________|                    |____________________|
>
> ______________                      ____________________
>               |                    |                    |
>               |--------------------|                    |------
>
>
> ---------------------|                    |--------------------|
>                      |____________________|                    |
>                       ____________________
>                      |                    |                    |
> ---------------------|                    |--------------------|
>
>
>
>
> this is how I am thinking to do it. Find out about the frequency first
> then based on that generate interrupt on every rising or falling edge
> then use one of the timer to control on time thru ADC or maybe it is
> better to use tables instead. Any help will appreciated


I think a good way to simplify this is by defining four states. Suppose
your top waveform is mapped to PORTB,0 and the others to PORTB 1,2,3. Call
your states: S0, S1, S2, S3. Define them as such:

S0  equ   0110b
S1  equ   1010b
S2  equ   0101b
S3  equ   1010b


(I'm assuming the the pulses are differential. If not, then you'll need
16 unique states).

Then to generate the above wavform:

  movlw    S0
  movwf    PORTB

  ...
  movlw    S1
  movwf    PORTB

  ...
  movlw    S2
  movwf    PORTB

  ...
  movlw    S3
  movwf    PORTB

  ...


This give you the flexibility to make this a state machine as well:


    cblock  ADDR & 0xfc     ; make sure lower two bits are zero

      _s0,_s1,_s2_s3

      curr_state
    endc

 ;Preload states
  movlw   S0
  movwf   _s0
  movlw   S1
  movwf   _s1
  movlw   S2
  movwf   _s2
  movlw   S3
  movwf   _s3

  ..



  ; Generate the waveform:

loop

    movf   curr_state,w   ; Get current state index
    andlw  00000011b
    addlw  _s0            ; Index into the valid states (note the addlw)
    movwf  FSR            ;Point to current state
    movf   INDF,W         ;get the value of the current state
    movwf  PORTB          ;drive the I/O's with it.


    goto   loop


Scott

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