Old 486 Board for ECU??

[Diehl, Jeffrey]

Two quick questions:

What is "PWM?"

and.

What do you mean by a "limited slip strategy?"

Thanx,

Mike Diehl,
MR-2, '87na

-----Original Message-----
From: Axel Rietschin [mailto:Axel_Rietschin at compuserve.com]
Sent: May 01, 2000 9:08 AM
To: diy_efi at diy-efi.org
Subject: Re: Old 486 Board for ECU??


----- Original Message -----
From: "Mike from West Australia" <erazmus at wantree.com.au>
To: <diy_efi at diy-efi.org>
Sent: Monday, May 01, 2000 20:35
Subject: Re: Old 486 Board for ECU??


> >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.

I was not referring to compensations. See my other posts.

>
> 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 :)

What about a limited-slip strategy?

> 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

Sure. But what if your AFM outputs a variable frequency signal, instead of a
0-5V signal?

>
> 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).

How many concurrent PWMs (that's the WHOLE point of this entire discussion)?
One is not enough. Consider that you have to fire the spark at the
appropriate time (assuming a DIS) and actuate a few valves in PWM all at the
same time.

> 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.

For your typical low-function-one-PWM ECU, it may. Motorsports ECUs uses 332
or even MPC555 microcontrollers with one or two built in Time Processing
Units, microcoded for time-related engine mgmt functions, plus a couple of
DSP chips for multi-channels detonation signal processing and, sometime,
dedicated chips like the 67F687 to help with engine timing issues. That's a
lot of timing-related hardware added to an otherwise standard CPU. The CPU
runs the high level control functions, PID algorithms for
closed-loop-everything and auxillary functions such as data logging. Again,
it all depends of where you want to go.

I'm not saying a 486 chip cannot do it. I say a PC won't be very good at
this ECU job, unless you complement it with a lot of stuff.

>
>
>
> Rgds
>
>
> Mike Massen
>


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