[Diy_efi] Re: Minimalist micro based EFI ?

[Bevan Weiss]

----- Original Message -----
From: "Bernd Felsche" <bernie at innovative.iinet.net.au>
To: "List for general do-it-yourself EFI talk" <diy_efi at diy-efi.org>
Sent: Wednesday, March 12, 2003 1:52 PM
Subject: Re: [Diy_efi] Re: Minimalist micro based EFI ?


> On Tue, Mar 11, 2003 at 10:08:52AM -0500, Grant Beaty wrote:
> > Seems silly to skimp on the processor though. My AVR Mega128 was a
whopping
> > $20, insignificant in the grand sceme of things.
> >
> > Do ECUs do a frequency -> digital conversion in hardware or software?
>
> What "frequency"?

I think that perhaps he was using one of the Ford (??) MAFs, that output a
PWM signal as opposed to a voltage...
Or maybe he was refering to retrieving the rpm of the engine.

Either way:
Whether it's done in software or hardware (note: both still require a
hardware timer) depends on whether the chip has the hardware to support
direct PWM->digital word conversion.  Many low cost micros don't and hence
large amounts of processing cycles are taken up waiting for the input to go
low and then timing how many clocks occur until it goes high again.  If the
software itself has to do the waiting/checking for the pulse then it's
software.  If the hardware can be programmed so that you issue a flag in a
register and it records (in a seperate register, normally) what the high
time/low time/period of the waveform was, then it's hardware...

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