Here is the PC board. The circuit only uses a small space.
The FET's for controlling the injectors are on the board.

The MM sends the control digital voltage to the six pin
dip D to A and it stores it until it is changed again by the MM.
It has a one or two wire serial interface.

That totally frees up time in the MM. You can change the pulse
width any time you feel like it. Every Rev or every ten revs.
It just keeps running on its own.

Unloads the MM to the point it can do a lot of other stuff.

The PC board cost is 3 for $50.

This is a MAJOR BREAK THROUGH in EFI,

Paul Lamar.


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Since the six pin digital to analog converter stores the voltage
from the MAF it is good to learn how the Maximite talks to it using
the I2C serial interface.

I2C requires a mere two wires, like asynchronous serial, but those two
wires can support up to 1008 slave devices. [ This of course is overkill
for our use as we only use one analog converter slave device.]


I2C can support a multi-master system, allowing more than one master to
communicate with all devices on the bus (although the master devices
can’t talk to each other over the bus and must take turns using the bus
lines). [ Again we don't need this feature but it comes with the chip.]

Data rates fall between asynchronous serial and SPI; most I2C devices
can communicate at 100kHz or 400kHz. [ This is important as you don't
want to use a lot of precious programing time
sending the MAF voltage to the D 2 A]

  There is some overhead with I2C for every 8 bits of data to be sent,
one extra bit of meta data (the “ACK/NACK” bit, which we’ll discuss
later) must be transmitted.

The hardware required to implement I2C is more complex than SPI, but
less than asynchronous serial. It can be fairly trivially implemented in
software. [This is irrelevant as the hard ware
is built into the Maximite.]


The big advantage of I2C is it only uses one or two Maximite pins. The
Maximite chip is not blessed with an over abundance of parallel ports.
One 8 bit parallel
port takes 8 pins of course. Some D2A 24 pin chips  require 8  or 16
pins. 16 bits would be 16 pins
and 16 wires or more for hand shaking. I know I built one of these systems.

Some later CPU's like the ARM used in some smart phones have as many as
200 pins.
However the wonderful Color  Maximite system is not available for them.
Yet :-)

The parallel connection however is very fast taking only one or two
micro seconds.

While the I2C may take 100 micro seconds or .1 millisecond for 12 bits.
12 bits is plenty of resolution for our MAF voltage. That is one part in
4096 parts.

A 16 bit par port would be one part in 64,000 which is way over kill
resolution for this application.

The parallel system is simpler in software  as all you do is store
voltage in one or two 8 bit ports.

The I2C takes some set up and then it becomes as simple.

Here are the Maximite I2C set up instructions attached in jpg form.

The complete EFI hard ware becomes stunningly simple
  with just two, one dollar,  tiny chips and an FET to turn on the injector.

At that point it does not need the Maximite unless you want to change
the power. The engine will run all day long at the same power as long as
it gets a pulse from the CAS. Another world record in EFI.

Paul Lamar


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