Re: Continuous Pulse-Width Measurement



<jawereq@xxxxxxxxxxx> schreef in bericht
news:Xns9641C69191956chickentonight@xxxxxxxxxxxxxxxx
> Hi,
>
> I'm wondering if anyone knows of a microcontroller or some cheap hardware
> in combination with a micro that can be used to continuously measure and
> buffer all of the high and low pulse-widths of a binary signal. I'd like
> to be able to buffer about 1000 16-bit width measurements in one shot.
>
> The catch is that the smallest pulse width measurable needs to be 700ns or
> better (500ns would be nice). I've looked at using an input capture pin
to
> a 20MHz or faster auto-cleared timer in combination with a DMA controller
> to transfer the captured pulse-widths to RAM, but all the transfer cycles
> generally add up to well over 1 micro-second. The 20MHz timer gives
> sufficient resolution, but the time to buffer the data is too long.
>
> Right now, the company I work for accomplishes this exact feat using an
> ASIC. Together, the current ASIC and micro cost about $7. Can the same
be
> done for less money, and possibly with a single chip?
>
> I appreciate anyone's suggestions on this problem.

16-bit width, 20MHz timer, that suggests the pulses are
between 500ns and 3ms. Is Ton + Toff constant? What are
you going to do with those 1000 measurements? Maybe there
is an entirely different approach to this problem, one
that does not require storing 1000 measurements.

Ubicom's IP2022 is extremely fast (120 mips), IP3023 twice
as fast, and both have enough ram to store your 1000 samples.


--
Thanks, Frank.
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