Homebrew PCBs

The printer that I am using has a serial clk of 4usec it is fast for a micro and I could not able to write a fast enough interrupt handling routine that can run on 8Mhz MSP430 micro. It can be different for your printer model.   
 I think in Eddie's solution micro works in parallel with cartridge chips, either he is sending complete zero for first 2 byte or reprogramming the chips (but I am not sure). In my solution I am completely emulating chips and not using the power source from the cartridge connection so I don't have any startup or power on reset problem. Sure new printers check everything, after writing it verifies the written data. If it fails, it gives error messages. I have tried to send same ink level; it accepts it after doing recharging (waste of ink). BTW Atmel has also very fast AVR series. 
   
Volkan  
....Have you tried always sending the same ink level back, or does the printer   notice if the value doesn't change?