Hi Michael,

you can use an 89C51 with the bootloader inside and connect a port pin with the EA pin.
Then the bootloader can write to an external Flash and switch the EA pin low to access this external Flash.


Or you use the T89C51RD2 or P89C668 or similiar, which have the bootloader and 64kB IAP Flash already internal. Then all 32 port pins are usable for your application.
On the P89C668 you can also use 8kB xdata SRAM internal. And on the T89C51RD2 are 1kB xdata SRAM and 2kB xdata EEPROM included.


Peter