Gordon,

You can do this with a 1-bit output direct-digital synthesis technique.


Given the following variables:

unsigned long increment_value;
unsigned long phase_accumulator;

for (some number of iterations)
{
    phase_accumulator += increment_value;

    // copy hi bit of phase_accumulator to output pin
    // code could look something like:
    movf    output_port,W               ; get existing port bit
    andlw    ~(1 << output_bit)       ; turn off current value
    btfsc     phase_accumulator;      ; is high bit on?
    iorlw     1 << output_bit            ; yes: turn the bit on
    movwf   output_port                 ; send it back to the hardware
}

The output frequency is directly proportional to 'increment_value'.

Bob Ammerman
RAm Systems


----- Original Message -----
From: "Gordon Varney" <gordonv@IAMNEE.COM>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Wednesday, June 05, 2002 4:37 PM
Subject: [PIC]: incrementing in steps


> I need a pin to clock out a square wave at 800Hz. Simple, just set pin
high for 625us, set pin low for 625us, and
> repeat.
>
> Now I need to increment the clock frequency by 50Hz, do some work and
increment by 50Hz again, continue incrementing
> until complete. The step duration in a time period is not a constant. What
is the best method to incrementing the
> frequency by 50Hz.
>
> (Note: I am using a combination of Assembly and the CCS compiler for this
program.)
>
> Gordon Varney
> www.iamnee.com
>
> --
> http://www.piclist.com hint: To leave the PICList
> mailto:piclist-unsubscribe-request@mitvma.mit.edu
>
>
>

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