Re: 6581 phase-accumulating oscillators

From: Steve Judd (sjudd_at_ffd2.com)
Date: 2000-11-20 17:17:10

Hola,

On Sun, 19 Nov 2000, Nate / DAC wrote:

> Yes, it does.  It achieves something like 33 kHz 8-bit stereo (with two
> SIDS) and I think somewhere close to 60 kHz in mono.  Since the SID can

I think there is a misunderstanding of what PWM is/how it works.  There
will be an article in the next C=Hacking on this very subject, which will
hopefully clear things up.

Regardless, I don't think this is what Richard was talking about.  He was
talking about modifying the frequency register to generate arbitrary
waveforms -- I think this is described in disC=overy issue #2.  For
example, take a triangle waveform.  On each cycle, SID adds the 16-bit
frequency value to a 24-bit counter, and outputs the upper bits of
the 24-bit counter.  So now imagine setting the frequency to some high
value, then zero, then some high value.  The output would look something
like

          *
         *
        *
   *****
  *
 *
*

i.e. a new waveform.  To answer Richard's original question, I have not
heard of anyone trying this, and would be interested in the result.

-Steve

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