GPIO (General Purpose Input/Output)

The General Purpose Input/Output (GPIO) peripheral is a fundamental feature in microcontrollers like the AVR series. It allows the microcontroller to interact with external devices such as LEDs, switches, sensors, and more. GPIO pins can be configured as either inputs or outputs, and their states can be read or written using specific registers. These pins offer a versatile way to communicate with the outside world, enabling a wide range of applications in embedded systems.

Tip If you're looking to better understand how to navigate and use my GitHub repositories — including exploring their structure, downloading or cloning projects, submitting issues, and asking questions, everything you need is clearly explained in this video: aKaReZa 95 - Programming, Git - PART B Make sure to check it out!
Caution It is absolutely critical that you carefully read every single word of this document, line by line, to ensure you don't miss any details. Nothing can be overlooked.

GPIO Registers

In AVR microcontrollers, GPIO functionality is controlled through several registers:

1. DDRx (Data Direction Register)

The DDRx register controls the direction of the GPIO pins. Each bit corresponds to a specific pin, and setting a bit to 1 configures the corresponding pin as an output. Setting the bit to 0 configures it as an input.

Bit	Pin	Description
0	PD0	1 = Output, 0 = Input
1	PD1	1 = Output, 0 = Input
2	PD2	1 = Output, 0 = Input
3	PD3	1 = Output, 0 = Input
4	PD4	1 = Output, 0 = Input
5	PD5	1 = Output, 0 = Input
6	PD6	1 = Output, 0 = Input
7	PD7	1 = Output, 0 = Input

2. PORTx (Data Register)

The PORTx register controls the output state of pins configured as outputs. Writing a 1 to a bit sets the corresponding pin to a high voltage level, while writing a 0 sets the pin to a low voltage level.

Bit	Pin	Description
0	PD0	1 = High, 0 = Low
1	PD1	1 = High, 0 = Low
2	PD2	1 = High, 0 = Low
3	PD3	1 = High, 0 = Low
4	PD4	1 = High, 0 = Low
5	PD5	1 = High, 0 = Low
6	PD6	1 = High, 0 = Low
7	PD7	1 = High, 0 = Low

3. PINx (Input Pins Address)

The PINx register reads the current state of pins configured as inputs. If a bit is set to 1, the corresponding pin is at a high voltage level. If the bit is 0, the pin is at a low voltage level.

Bit	Pin	Description
0	PD0	1 = High, 0 = Low
1	PD1	1 = High, 0 = Low
2	PD2	1 = High, 0 = Low
3	PD3	1 = High, 0 = Low
4	PD4	1 = High, 0 = Low
5	PD5	1 = High, 0 = Low
6	PD6	1 = High, 0 = Low
7	PD7	1 = High, 0 = Low

Example Code

Note

The macros used in the code below are all defined in the aKaReZa.h header file, and detailed descriptions of these macros can be found at the following link:
https://github.com/aKaReZa75/AVR/blob/main/Macros.md

#include "aKaReZa.h"

/* Configure PD0 as output and PD1 as input */
GPIO_Config_OUTPUT(DDRD, 0); /**< Set PD0 as output */
GPIO_Config_INPUT(DDRD, 1); /**< Set PD1 as input */

bitSet(PORTD, 0);  /**< Set PD0 to high */

/* Check if the bit 1 of PIND is high */
if (bitCheckHigh(PIND, 1)) 
{
    bitWaitLow(PIND, 1); /**< Wait until bit 1 of PIND goes low */
    bitToggle(PORTD, 0); /**< Toggle the bit 0 of PORTD (change the state of pin 0 of PORTD) */
}

Additional Notes and Common Pitfalls

1. Input Configuration: When configuring a pin as an input, ensure that the corresponding bit in the DDRx register is set to 0. If you accidentally set the pin to output and try to read from it, the value returned will not reflect the actual pin state.

2. Internal Pull-Up Resistor: If you need to use a pin as an input and you want to avoid floating states, you can enable the internal pull-up resistor by writing a 1 to the corresponding bit in the PORTx register. This is useful when no external resistor is connected to the input pin.

   /* Enable internal pull-up resistor on PD1 */
   bitSet(PORTD, 1);  // Enable pull-up on PD1

3. Avoid Writing to Input Pins: Writing to a pin configured as input will have no effect, but it may cause confusion if you mistakenly attempt to do so. Ensure that you only write to pins configured as outputs.

4. Debouncing Buttons: When reading inputs from mechanical switches, be aware of button bounce. Consider adding a delay or implementing a software debouncing mechanism to ensure accurate reading of the button state.

5. PINx for Input Only: The PINx register should only be used to read the state of input pins. Reading from output pins with PINx may give incorrect results as it returns the last value written to the PORTx register.

6. Port Pin Conflict: Be mindful of pins that may serve multiple purposes (e.g., a pin that is both an SPI pin and a regular GPIO). Check the datasheet to ensure proper pin configuration to avoid conflicts between functions.

🔗 Resources

Here you'll find a collection of useful links and videos related to the topic of AVR microcontrollers.

Tip

The resources are detailed in the sections below.
To access any of them, simply click on the corresponding blue link.

• AVR Microntroller

  This repository contains comprehensive resources for AVR microcontrollers, including hardware schematics, software libraries, and educational projects.

 AVR, GPIO
   ├── [aKaReZa 20 - AVR, GPIO - Part A]
   │   ├─ Output Config — GPIO registers and pin setup.
   │   ├─ Simulation — Proteus + LED control in PlatformIO/VSCode.
   │   ├─ Timing Sync — Fuse bits vs compiler clock.
   │   └─ Macros — Improving code readability.
   │
   └── [aKaReZa 23 - AVR, GPIO - Part B]
       ├─ Input Config — GPIO registers and pin reading.
       ├─ Simulation — Input handling in Proteus + PlatformIO/VSCode.
       ├─ Pull-Up — Enabling and using internal resistor.
       └─ Logic Control — Handling input with `if` statements.

aKaReZa 20 – AVR, GPIO - Part A Introduction to AVR GPIO control registers, pin configuration, simulation in Proteus, coding in PlatformIO and VsCode, timing issues, and code readability improvements using macros.
aKaReZa 23 – AVR, GPIO - PART B Learn about AVR GPIO control registers, configuring pins as input, reading pin status, simulating AVR in Proteus, coding in PlatformIO and VsCode, using internal pull-up, and using if statements for input.

💻 How to Use Git and GitHub

To access the repository files and save them on your computer, there are two methods available:

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Clone using the URL.

First, open Git Bash :

• Open the folder in File Explorer where you want the library to be stored.
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Note

If you do not see the "Open Git Bash here" option, it means that Git is not installed on your system.
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• Once Git Bash is open, run the following command to clone the repository:

git clone https://github.com/aKaReZa75/AVR_GPIO.git

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Important

Please keep in mind that the numbers displayed in the image might vary when you perform the same actions.
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Note

Advantage of Cloning the Repository:

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Important

• No Updates: Keep in mind that downloading the repository as a ZIP file does not allow you to receive updates.
  If the repository is updated, you will need to download it again manually.
• Ease of Use: This method is simpler and suitable for users who are not comfortable with Git or command-line tools.

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Tip

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