Hey! I would like to ask, can i upload code to external EEPROM. I tried to make i2c lock (mcp23017 + 1602 + keypad), but it didn't fit to my Attiny45 of course... The code took me 10KB, and Attiny has only 2K. So is it possible to write code to external EEPROM? I think it is possible, but little too hard to make. Little advise is needed! 
I have ordered Atmega328 (yeah, with bootloader), but if it's possible to run code from external memory, i'm going to do it (if it's not too hard...).
No
Mark
The GOOD news: Yes, you could easily load code to an I2C EPROM (at which point, it becomes DATA).
The BAD news: Oops, because it is now DATA, you can not execute it as program instructions under Arduino's architecture.
Sorry, but good thought process to solution, under a different architecture.
Is there any microcontroller, that can read code from external EEPROM and run it? Or maybe even clear it's own memory and download new from EEPROM? Or can i use other kind of memory? EEPROM is pretty short life memory. Some chips has over million write cycles, but it will corrupt anyway sometimes.
Google "Manchester" and "van Neuman"
what you want to do would work with a microcomputer (they use the same memory space for instructions and data), but not a microcontroller (the few that I am familiar with, use separate memory spaces for data and for program instructions).
I think Von Neumann architecture would work with this kinda project. Is there any "development board" with Von Neumann architecture?