Probably the easiest way for me to explain
EFI software is to look at the early
Megasquirt software written in straight forward
assemble language. Assembly language is a very mechanical
thing. It is well adapted to controlling mechanical
devices. Assembly language is close to a one to one correspondence
between computer instructions and computer operations. Assembly language
programming also gives direct access to key machine features such
as sensors and injectors.

Computers are set up like post offices. There
are many numbered boxes. Each box is an address.
The boxes can also have names such as "bank".
It is easier for the programmer to remember
"bank" than box #8765. These boxes are also
known as memory locations.

MAP sensors look just like a PO box after the analog
data is converted to digital. The analog to digital
converter (ADC) is a black box electronic device that takes
in a zero to 5 volt analog voltage and puts a number 0 to 64
into a PO box maybe called the MapSensorBox. This is called
memory mapped Input Output or I/O for short.

Let me give you a simple example.
The LDA instruction moves 8 bits of data (65 combinations of
eight zeros and ones 01001110) from one specified box to another.
Here is what it looks like on paper in the program listing.

LDA MapSensorBox

Translated it means LoaD (really copy) what is in the MapSensorBox
to another box called the Accumulator box. This instruction
could take way less than one micro second (usec) to complete
in a fast computer. One will know exactly HOW FAST in case
time to achieve something is important to one. That is
usually the case when controlling a high speed machine
such as an engine.

This is probably the most frequently used instruction
you will find. With several more simple instructions
like this, one can write programs that do useful things.
Especially if one is controlling a machine.

That is all there is to it. No more complicated than
that. In the next lesson we will cover the STA instruction.
Another highly used instruction.

Paul Lamar

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