Old 486 Board for ECU??

[Mike from West Australia]

At 07:07 AM 1/5/2000 +0200, you wrote:

>> Of course you need an ADC but only one of the inputs could be
>> considered as time critical and even that (AFM) can be asynchronous
>> with respect to engine cycles... ie Fast sampling helps but
>> AFM synchronous measurement is not required...
>>
>> my 2c worth.
>>
>
>You are describing a very simplistic ECU. Why not put one sensor where you
>want your injection pulse to begin, and another where you want your spark to
>fire? With a little cleverly designed analog circuitry, you probably don't
>need a CPU at all ;)

Yes thats true but realise they are *all* based on a similar functional
model and yes a simple piece of analog circuitry can do EFI quite well.

I would also add you do *not* need complex timing for very sophisticated
ECU's with lots and lots of compensation factors. With any engine you
'only' need to determine fuel injection pulse width in concert with
compensation factors. Main input is going to be AFM and speed with
adjustment by engine temp - effectively thats it.

If you want more smarts it will need more ROM not more timing.

Your average 68HC705R3 will do 6 cylinder sequential injection and
handle a MAP as well as MAF if you wanted :)

Whats important for high end compensation is how fine can the
injector PWM resultion reach and is it within the error margin for
the AFM or MAP inputs and what sort of averaging do you use for
the O2 sensor etc

Around late 80's I did a systems model using the 68HC705R3 with a little
external EEPROM - you could do heaps of compensation using maths in
the background (non interrupt) whilst preparing PWM time constants
for the foreground (interrupt driven).

So all this hogwash about 486 boards not having timing is a software
issue around MSDOS not any limitation of the motherboard - the hardware
is much more capable then it needs to be with the exception of ADC's.



Rgds


Mike Massen

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