Erik - the 'ancient' AT28C256 does not require 12V - it is a 5V eeprom (not even flash!). The cost of this device would most likely exceed that of a modern cpu with integrated flash.


Mike - your 80C51BH will most likely not operate at 18.432mhz, the fastest parts I recall were the -1 at 16Mhz.

It sounds like you want the cpu to be a smart address counter to make your circuitry easier. Sure,you can do it by jamming instructions into the cpu like NOPs and slowly clocking it, but how do you know the current state of the cpu without polling the ALE or whatever? And you'd have to isolate the data bus with a '245 or whatever. Taking this concept a little further, there's no reason why you can't use the cpu to generate the address and the timing for you and getting rid of a lot of '245s etc. You just need to have some code that gets loaded into ram or have an eprom with the code to do what you require.
Unfortunately, I've just redesigned your whole concept.

What I did on a product I designed many years ago is to have a large flash eeprom (128kbytes) and add some extra logic that allowed me to swap between the two halves of the flash. The top half(64k) had bootloader code, this ran first and checked a pushbutton. If the pushbutton was not pressed,it would swap to the lower half of the flash and run the program, otherwise it would run the bootloader code that would allow me to download new code via the serial port. Just a few seconds and I had new code loaded. You could do something similar with your eeprom.