Noise from points ignition

[Walter Petermann]

I am designing a system based on a Motorola HC12
>> and need to know if the noise from points ignition will cause problems.

Hellow Chris,
my name is Walter Petermann. I have just recently gotten an internet
account and joined this discussion group.
I have a home business repairing fuel injection computers for Jaguars
and I have a general interest fuel injection systems along with a few
years background in electronic design.

I have not followed the thread of your messages to the group, but based
on what I have read today, here is some input which may/may not be
usefull to you.

On the Jag (V12 80's) there are separate systems for the fuel injection
and ignition. The fuel injection brain (ECU) uses the signal from the
negative terminal of the ignition coil to generate the timing for the
injectors. There are twelve injectors split into two banks of six. Every
six 'ground pulses' that the ECU senses on the coil negative,
it fires one bank of the six injectors.

The ground pulse sensing cicuit is as follows:
The negative coil terminal signal goes through a 22K resistor into
both inputs of a nand/schmitt trigger gate. The output of the gate
is tied directly to the microprocessor.This gives a positive pulse to
the uP during the time the ignition system has the coil grounded.
The inputs of the nand gate are protected by a 5.1V zener to ground, and
a copacitor ( which is too small for me to read the numbers off of..) to
ground.

The nand gate chip is an RCA  CD4093BE
Hope this was helpfull,
  Walter