SWITCHED EPROMS

[Frederic Breitwieser]

>i have found the these to work fine in the P4 and also in TECH-1
>cartridges.  if you use the same base code and only change the data of

I liked your design, however I wish to submit the following comments.
Instead of using SPST switches directly attached to the E/Eproms, its
important to make them bounceless, whereby when switching, the real
millisecend on/off/on condition assiociated with mechanical switches is
therefor eliminated.  I have a schematic in my archive I can share, when I
get home, not a problem.

Then, after making the switch bounceless, you use either a Flip-Flop
circuit or four inverters to control the enable lines of the two eeproms,
which you are correct, can only have the data set information changed, not
the actual code.

A friend of mine who designed embedded systems for a career, has such a
system that actually allows CODE changes... this is because, the main loop
of the program always starts at one particular address, on both chips, then
the processor switches the enable pins on the EEprom, not a mechanical
switch.  The mechanical switch controls one of the inputs on the processor,
when when it hits the beginning of the loop, where the code is the same in
both chips, will enable or disable the appropriate eeprom.

Just some thoughts :)


Frederic Breitwieser
Homebrew Automotive Mailing List
Bridgeport, CT 06606
http://www.geocities.com/MotorCity/Downs/4605/index.html
1989 AG Hummer 4-Door
1993 Supercharged Lincoln Continental
2000 Mid-Engine Sports Car <smile>





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