On Sat, Oct 30, 2010 at 10:54:37PM -0700, Kirk Wallace wrote:
> Apparently the XMega's use JTAG and PDI for programming. My programmer
> doesn't support either. Newer programmers should be okay and aren't that
> expensive, but it is something I need to consider.
Yeah, my old STK500 won't cut it either. A "JTAG ICE" is several hundred
dollars, and their "AVR ONE" is twice that. :-(
> When I played with RC filtering PWM to get an analog signal, I used
> software stepping through the parport and got lousy results. So I wrote
> that idea off. Since then I've learned a little bit more and it seems
> lots of people are using it successfully. I think one needs either a
> higher frequency or use PDM instead.
To allow the integrator to work well, you need to maintain a constant
high frequency, and just alter the duty cycle. (mark/space ratio) The
higher the frequency, the easier it is to low-pass filter, yet not have
to wait for the analogue output to respond to a large step input.
A microcontroller's PWM channel does that easily.
If your PDM is "Pulse Duration Modulation", then that's fine, but
wikipedia's "Pulse Density Modulation", isn't what's needed, at all.
Erik
--
Never worry about theory as long as the machinery does what it's
supposed to do.
-- Robert A. Heinlein
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