Oversized EPROM's & Multiple Programs

[k1drbar]

... assuming that all that you are doing is running the same code with different maps, it could well
be possible to change programs on the fly ... but you would really have to understand the circuit
and make sure that the address line that switched banks only changed at an appropriate time.
Perhaps it would be as simple as a register ... here again, assuming that the code was identical
other than the maps.  All that said, you might want to have some means of not switching the map
except when the ECU is executing the idle loop ... which would take a bit more hardware complexity
...

... what I do is to use a latch that samples the state of the selected binary when the ECU is
powered up.  To switch to a different binary you need to shut the car off and restart it.  In my
case there really isn't a need to be able to switch the code on the fly ...

HTH!
Steve Buchholz
San Jose, CA (USA)

----- Original Message -----

To those who are using, or have used, oversized EPROM's that contain more than one program
image........

Can you simply select between say Program "A" and Program "B" while on the fly, or do you have to
power/idle down and then switch from one to the other?  This would be for a two program solution in
place of a single 27c256b chip, for a friend who has new young drivers in the family (think of it as
a sort of valet mode).  Is more than 2 images a big hassle in place of a 256 chip?  The selector
switch would be a keyed Allen Bradley jobbie.

Anyone have any interesting tidbits archived on this topic, on their HD's, that they can pass along?
I'm going to dive into the list archives over the next few nights, but any direct pointers would
certainly help a bunch.

Walt.


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