Precautions for using AVR microcontroller I/O ports-EEWORLD

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1. Correctly set the DDRx direction register before performing read and write operations on the I/O port.

2. The initial state of the I/O port after reset is all input working mode, the internal pull-up resistor is invalid, and the external pin is in a three-state high-impedance input state.

3. When the I/O port works in input mode and you want to read the level on the external pin, you should read the value of PINxn instead of the value of PORTxn.

4. When the I/O operates in input mode, use or not use the internal pull-up resistor according to the actual situation.

5. Once the I/O port's working mode is set from output to input, you must wait for 1 clock cycle before you can correctly read the value of the external pin PINxn.

Reference address：Precautions for using AVR microcontroller I/O ports

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