Correction: The $2.50 MC9S08 with the analog to digital converter is 16
pins and not 14.  We may get it smaller later on if I can get a cheap
programmer.

This chip does not have a pulse width modulator so we are going to do it
using a timer.

How that works is as follows you load the timer with a number that will
give the desired pulse width. You then set the output pin high. When the
timer times out you set the pin low. You then wait until it is time to
send out another pulse and do it all over again.

A simple way to wait is to feed  an oscillator into the reset pin of the
chip running at a desired fixed frequency for triggering the injectors.
It then takes in an analog voltage from the MAF and goes through the
motions of setting the timer and so fourth to output the pulse width.

Things happen so fast, on the order of 20 million instructions per
second, the inherent delays in doing this are minimal. With an
oscillator with a 10 ms period (100 CPS) 200,000 computer instruction
can take place if my arithmetic is correct. Max pulse width would be 8 ms.

What this also does is make the microcomputer software  crash proof as
it is always starting from a reset condition for each pulse.

The chip requires only two capacitors. Less parts than a 555.

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I discovered a built in fixed frequency oscillator in the chip. Saves building an external oscillator.

The choices are 31 cycles per second (32 ms) or 125  cycles per second (8 ms). What do you electronic types think? Is 32 ms often enough to squirt fuel? The advantage is it gives a wider dynamic range and better resolution for the injectors at a given fuel pressure.

I suppose I could count cycles giving a 16 ms option using every other one.

Paul Lamar