[Diy_efi] Another Eprom Question

[David Cooley]

 Back in 87 I was running a 27C512 with 4 programs on my Buick GN...
had a small board the chip was on and a shielded ribbon going to the ECM. 
would toggle the 2 highest address bytes with a thumbwheel on the dash to
change banks and did it on the fly all the time with no CE light.

 
-------Original Message-------
 
From: mbelloli at speedymotorsports.com
Date: 01/25/05 15:13:07
To: diy_efi at diy-efi.org
Subject: [Diy_efi] Another Eprom Question
 
Hello everyone,
I have been pulling my hair out trying to figure out another one of
these chipping ideas. I am trying to set up a controller to allow
the switching of which chip the ecm of a car computer is running on
the fly while driving. Currently I've got it working very well if
you switch with the key off, but not while running. The original
chip was a 27C256, which switched out for an ATMEL AT29C010. I
really only wanted 4 choices, which this chip more than allows. I am
trying to set it up so I can have pic processor do the switching for
me. I cound't put a picture of the waveform that is driving me crazy
here so I put it on my website at
 
https://home.comcast.net/~hexibot43/ChipEnableLogic.htm
 
I just can't understand why it is working right now with the signal I have
on the Output enable pin. From what I understand it shouldn't be working,
but it is working. I thought I was going to simply look at the signal,
and see drops to ground like I did with the last car computer I looked at.
I figured I could use that as a trigger for an interrupt the would in
turn wait a set amount of time and then switch banks. This way I could do
the switching when the chip was not be read from, and so the ecm would be
happy and not throw an check engine lamp at me.
Can anybody sheld some light on this for me? You guys did so well
helping me last time, I hope you can do it again. And yes, I still
have a lot more to learn.
 
Thanks,
 
Marcello
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