I am using the AT89C51 which has 64k of internal programming space but I need more. I can use the PSEN* line to use external memory so two questions: 1) if I add 64k, can I continue to use internal memory and have 128k available. 2) If I lose the internal memory, can I add more than 64k external?
Something like the AT89C51CC03 ?
My recollection of 8051 architecture is that to get beyond 64KB you have implement some sort of paging/banking scheme. This does significantly complicated the HW and SW
In 2020 you might want to consider a design refresh using better/cheap MCU based on ARM cores.
If you can't migrate that far, perhaps there are some SiLabs offerings
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