Data Sheet

Automatic (Software) Reset
Rather then requiring a physical press of the reset button before an upload, the Arduino Nano is designed in
a way that allows it to be reset by software running on a connected computer. One of the hardware flow
control lines (DTR) of the FT232RL is connected to the reset line of the ATmega328 via a 100 nanofarad
capacitor. When this line is asserted (taken low), the reset line drops long enough to reset the chip. The
Arduino software uses this capability to allow you to upload code by simply pressing the upload button in the
Arduino environment. This means that the bootloader can have a shorter timeout, as the lowering of DTR
can be well-coordinated with the start of the upload. This setup has other implications. When the Nano is
connected to either a computer running Mac OS X or Linux, it resets each time a connection is made to it
from software (via USB). For the following half-second or so, the bootloader is running on the Nano. While it
is programmed to ignore malformed data (i.e. anything besides an upload of new code), it will intercept the
first few bytes of data sent to the board after a connection is opened. If a sketch running on the board
receives one-time configuration or other data when it first starts, make sure that the software with which it
communicates waits a second after opening the connection and before sending this data.
https://store.arduino.cc/datasheet/index/index/url_key/arduino-nano/
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27.09.2019, 09:10