Robert Lacoste wrote:
.....
>Dan, regarding RAM size, my code was originaly
>developped for the 17C756 (>900 bytes of RAM) and was
>adequate for a 128 words FFT, calculated in 50ms.
>Could be of course extended with external RAM.
>And yes I have a (very small) web site. My FFT code is
>not available there, but you will find my freeware
>17C756 programmer : //www.geocities.com/robert_lacoste
>
>Cheers,
>Robert.
>

Robert, thanks for responding.

Let's see, 128 bytes/input, plus 2 x [256 for real/imaginary]
= 640 bytes, or 768 if 12-bit input data. Doesn't leave any
left for double buffering or output buffering, if you wanted
to do real-time pass-through. And this on a 68-pin, $16 chip
with hardware multiplier. Guess that's why I never tried it
on a PIC before [but always wanted to].

However, the new 18C252 is faster, cheaper, with fewer pins
(28-p) and more RAM with linear addressing. With 1536 RAM bytes,
you can just squeeze in a 256 FFT: 256 + 2*[256+256] = 1280
bytes, if 8-bit input data. Probably could not utilize the full
10-bits of the '252 A/D here. But could probably do 128 FFT with
real-time double-buffering, and pass-thru.

Now, we need someone with a freeware 18C252/452 programmer, and
DSP code library personalized for it.

Thanks much for the info, and best regards,
- Dan Michaels
Oricom Technologies
http://www.sni.net/~oricom
==========================