EFI algorithms

[Pete Sterrantino]

At 10:08 AM 6/12/96 -0700, you wrote:

>First off the handle Map. In the past I have used an OEM Map sensor
>This gives about 4.75 volts at wot and about 1.5 volts at idle
>or 18 inches of vacum. In the past this was fed into the AD and
>I used the resulting conversion in the code directly. What
>I need to do now with new software is to develop a load factor
>between 0 and 255. Whats the best stragedy. A calculation using
>to A D value or a lookup table or a search. Once you have the
>load factor between 0 and 255 a divide by 16(four shifts right)gives
>you the index for your lookup table.
>
>Second RPM.
>In the past I used the input capture to give me the time value between
>two ignition pulses. A division of the highest RPM about 400 rpm 
>increment at 6400 rpm in timer value would give me a table of
>15 rpm increments plus if you use idiv a fraction is also created.
>My four point interpolation would use map fraction and rpm fraction
>to smooth the values in the lookup table.
>What I wish to do is use a 25 rpm increment at 6400 rpm to create 
>a rpm table that runs in 25 rpm increments between 25 and 6375 rpm.
>Since I am currently working on idle control I need the finer resolution.
>Also I have decided to split the look up tables into a lower load
>lower rpm table and a higher load higher rpm tables. The lookup indexs
>for the low load rpm table would be finer increments. This would
>make low rpm operation much better.

Peter:

I'm not sure what you are really trying to do but i'll make some suggestions
anyway. 
1. The 68HC11 A/D converter can be scaled in hardware.  If you set Vrl to
1.5 V and Vrh to 4.75 the 3.25 V difference would be across the 0-255 range,
i.e. 0.0127 volts/bit.

2. If a hardware change is not possible, and memory is not a problem, a
lookup table is the way to go. It's much faster.

3. If memory is a problem, you may want to find a function that defines your
data and calculate the answer each time.

I can't see what you're trying to do in the second part.  Maybe if it were a
little clearer...Or I could look at the code.  The idea sounds ok.  Is there
a problem with timer resolution?

Hope this helps...

Pete S.