![]() ![]() There should be some care when using PORTD and Serial/USART because pins 0 and 1 from the PORTD are the ones used by the USART and if you put both of them as inputs or outputs the USART may be unable to read or write data in those pins. As every logic value, each bit in the DDRx registers can be either 1 or 0, being that putting a specific bit of DDRx at 1 configures the pin as output and putting it at 0 will configure the pin as an input, lets see a small example that configures pins 0,1,2,3 as digital inputs and pins 4,5,6,7 as digital outputs:Īnd if you need all outputs? Try it yourself, or wait a few days and I will release my bit-manipulation tutorial. Well, to begin there is a dedicated register for each PORT that defines if each pin is a input or an output, that register is the DDRx, where x is the letter from the PORT that we want to configure, in the case of the Arduino there is DDRB, DDRC and DDRD. So, how can we interact with our digital pins? In this image you can see all the alternative functions that each pin can have, the chip in question is the Atmega328p.Īnd here is the mapping between arduino port names and their real name: Our micro-controller, the Atmega328p as registers, those registers are associated with the input/output ports, each port as a specific name and the associated registers, in fact our atmega as port B,C and D, and each port as a different number of pins(this is a restriction of the 28 pins PDIP package and not from the micro-controller, because an 40 pins PDIP for example as 4 ports with the full 8 bits each one), the only port that as the full 8 input/output pins is PORTD.Īs you may already know, each pin can have multiple functions, like pwm generation, or ADC capabilities, the pins 7 and 7 from PORTB are also the input pins for the crystal oscillator, and pin 6 from PORTC is the reset button. You can also use the constants LOW, which maps to 0, and HIGH that maps to 1.Hello fellow readers, today I will write a bit about the digital pins and how to read and write digital values to then, its a simple subject but of a great importance, because almost everything that our micro-controller does is using its inputs and outputs to talk with leds, motor drivers, lcd’s, shift-register, to read data from digital sensors and a lot other things, so lets start reading about how to do it. If the button is not pressed, Arduino will detect 1. If the button is pressed, Arduino will detect 0. This value can be 0 or 1, depending on the input. Then in the loop() function we get the value of the input pin using the digitalRead() function: int value = digitalRead (BUTTON_PIN) If nothing is connected, it defaults to 1. In the circuit we could add a pull-up or a pull-down resistance, but it’s easier to pass the INPUT_PULLUP flag to Arduino. The INPUT_PULLUP option is needed because by default if nothing is connected to the pin (if the button is not clicked, the circuit is open and it’s like nothing is connected to the pin), the input pin is floating, which means it’s subject to interference and it can randomly pick a 0 or a 1. In the setup() function we call pinMode() to set this pin as an input pin, with the INPUT_PULLUP option: pinMode (BUTTON_PIN, INPUT_PULLUP) We define the pin number as a constant to avoid having a magic number in our code: #define BUTTON_PIN 3 We’ll detect the voltage level on pin #3 every second. We’ll have a button that has one lead connected to GND on the Arduino, one lead to the digital pin #3 (any other digital pin would work). We’ll first build the circuit, then we’ll switch to the Arduino IDE on our computer. ![]() They are numbered from 0 to 13, but you will almost always skip pins 0 and 1 unless you run out of pins, because they are used for serial communication (see the rx and tx labels printed on them). In this project you’ll learn how to read from a digital I/O pin, using the digitalRead() function.ĭigital I/O pins on the Arduino Uno board are the ones on the USB port side of the board, and they might also be marked as digital on the pins, like in my case:
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