I would use a hardware device, such as a FPGA for the 80Mhz work. Then 
I'd use a cheap PIC
to interface to the FPGA and buffer to an RS232 or USB/Serial Host.

The FPGA would need to identify the start of a pulse, trigger  the three 
sample/holds, and  tell the
PIC when to  capture quadrature tach signals. Quad tach is trivial to  
decode in a standard PIC.
It would probably be doable with a 20Mhz PIC16F88. The PIC can even read 
the sample/hold
A/D data. The FPGA would have to be clocked at 80Mhz of course.

BUT...

an SX (Ubicom) device could do it all within the single CPU chip. An SX 
chip is very fast, running
4x the speed of a PIC using the same clock speed. SX chips can handle a 
75Mhz clock; the same
PIC would have to run at 300Mhz. That might be a fun project.

--Bob

Les Elkins wrote:
> Hi folks,
>
> I'm a new person to pics. By background I'm a software guy with a smattering
> of hardware many years ago. Lately I've been tasked to look for alternatives
> to a data capture board. We think we can make something cheaper and much
> better than what we have.
>
> The gadget I have to interface with has the following traits:
> 	-A pulse-width-modulated signal coming out at 80MHz
> 	-Three analog lines
> 	-An encoder on a spinning wheel.
>
> The pulse signals come along at up to about 5KHz. When a pulse happens, I
> need to 
> 	-Grab the width, measured with an 80MHz clock
> 	-Grab the three analog values
> 	-Grab the encoder value
>
> This data must be buffered and streamed out to a host.
>
> I've been reading data sheets and it seems a dsPIC33FJ128MC710 might be a
> decent choice: Quadrature encoder, decent amount of RAM to buffer stored
> data, and enough A/D to easily get the analog data. 
>
> However, it's only running at 40 MIPS, and my signal is 80MHz. As I'm
> reading the data sheets, I see reference to running the Type A Timer in
> asynchronous mode from an external source. I haven't found anything that
> tells me if this external source can be 2x the CPU clock speed.
>
> So.... Can someone tell if this is a valid approach (or tell me which
> documentation I should be reading to determine that)? If this won't work I
> assume I could add an external timer- would this be a reasonable approach
> for this soft of signal?
>
> My hope is to demonstrate the validity of this approach using the
> downloadable Microchip tools. If that works I can get an electronics type
> with appropriate hardware background to support me in this project.
>
> It's been quite a while since I looked at PICs for any projects. I'm
> impressed with what's out there and the clock speeds- my last glance into
> this area only low-speed chips were available.
>
> Thanks,
>
> Les Elkins
>
>
> Les Elkins
> Spatial Integrated Systems, Inc.
> Rockville, MD
> www.sisinc.org 
> les.elkins@sisinc.org
> 301 610 7965 x107
>
>
>
>   

-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist