EMI and logic families

[John S Gwynne]

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   Before I start construction of my CPU board for my engine controller, I'm
interested in the experience that others have had with EMI.

past experience:

I have used the HCT logic family IC's with no problems even within a foot of
an MSD 6 without the optional "noise" filter. I have been using wire-wrap
with no ground plane and no additional shielding. Unfortunately, these
devices are sloooooow....

I have also used National Semiconductor's GALs, but I have had EMI problems
with these. I found that wires of more than 3 or 4 inches in length would
pick-up enough noise (what appears to be energy above 100MHz) to "screw
things up". I would think that a ground plane and a shielded enclosure would
cure this, but since I'm working on a first generation proto-type I've
elected to slow the devices by simply adding series resistance right at the
input pins (I did not need the speed; just the convenience of a GAL).  This
seems to work an does not obscure access to the boards.

new concerns:

I now want to add a semi-fast 16-bit CPU using ALS, GAL, and maybe even AS.
This is going to be tough to build via wire-wrap in the first place let alone
in the presents of a MSD ignition module.

My question to the group:

Have other encounter similar problems? Has anyone used ALS or AS with a MSD
ignition module nearby? What have you built and what logic families have you
used? How much shielding?

                                       John S Gwynne
                                          Gwynne.1 at osu.edu
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