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what you need to do is to place the boot program at the end of the extenal e2prom by a programmer, the boot pgm will initiate the serial comunication with the pc to program the e2prom from the begining, you need to do a hardware activities to enable writing to the e2prom while reading instruction.
and also you need to add to your program at statup:
reset: jz p1.0,boot_adress
witch enable you to enter the boot pragram after you lowed p1.0 at reset.
Some chips from DALLAS SEMICONDUCTOR have internal ROM which you can switch off with your software, so you can load program using ROM bootstrap loader, then jump to this program and switch off ROM and finally move your program to begining of RAM - DATA and PROGRAM memory must reside in the same ram area ...
Of course some versions have EPROM and even FLASH ...