after update software on my arduino Nano board via ICSP i can't use USB for serial monitor and update software, why?
closed as unclear what you're asking by jfpoilpret, Michel Keijzers, Enric Blanco, Code Gorilla, Greenonline Jun 1 '17 at 4:49
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Assuming you have reprogrammed the Arduino Nano's Atmel processor (an ATmega328) directly using the processor's ICSP pins, you may have erased the Arduino boot loader from the processor. In such a case you no longer have an Arduino. Rather you have an ATmega328 processor surrounded by some hardware.
To recover you need to reprogram the ATmega328 processor with the Arduino boot loader.