ARG! I just lost my message because I pressed the QUOTE TEXT button instead of the POST button!!! Craig, please fix or separate that condition.

Mak,

There is no feasible way to run the program out of a serial Eprom. The 8051 will only run code from its internal codespace or from its parallel data bus from external Eprom or RAM.

The only marginal interpretation of the request is to load and run hidden code loaded in a serial Eprom. Applications for this are to deceive anyone attempting to steal your code and design, and for hackers to hide 8051 viruses assuming they have a loader mechanism in the rest of the code.

In this interpretation, you must have the 8051 read the hidden code from the serial EEProm and load it into external parallel RAM. If the RAM is mapped so it can be read with a PSEN signal, then you can accomplish this.

HOWEVER, if you want security then you're better off with all of your code in an OTP 8051 (One-Time programmable) with all the unused bytes zeroed out and the security bits burned so that no code can be read OR APPENDED. This is still the best protection for IP (intellectual property) that your competitors would attempt to copy and analyze.

FLASH 8051 is getting better at protecting IP than the first series which unwittingly let you append new code without first erasing its entire memory. That might sound like a silly requirement (to erase everything first, always) but if you don't, someone could append a new routine to read all the code space and dump it down the serial link. :)

aka j