PV198 - GPIO
One-chip Controllers
Daniel Dlhopolček, Marek Vrbka, Jan Koniarik, Oldřich Pecák,
Tomáš Rohlínek, Ján Labuda, Jan Horáček, Matúš Škvarla, Ondřej Bleha,
Martin Klimeš, Adam Valt
Faculty of Informatics, Masaryk University
2/2024
Content
Content
GPIO Overview
Buttons
Debouncing
Application
LED using SDK example
Button using config tools
Homework
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GPIO Overview
Have you checked the preliminaries in study materials?
Do not forget to setup a new branch for this week (Week_02)!
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GPIO Overview
What is GPIO
GPIO – General Purpose Input Output
Direct control of pins of the MCU
Basic interaction with external world
Can be programmed as input or output
Has only 2 states (logic 0, logic 1)
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GPIO Overview
What is it used for
Anything that works with 2 states – on/off
LED
Buttons
Sensors
And used by more sophisticated peripherals
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Buttons
How buttons on board work
Connects pit to ground (logic 0) or to voltage (logic 1)
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Buttons Debouncing
Button debouncing
Bouncing
Looks like button is pressed multiple times
Cause by mechanical contact of the switch
Solution
1. HW debounce (add capacitor)
2. SW debounce (wait few milliseconds)
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Application LED using SDK example
Steps required to create an application
Initialize (MCUXpresso Configuration Tools help here)
1. Pin
2. Clocks
3. Peripherals
Write application code
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Application LED using SDK example
Peripheral configuration options
1. Write everything from scratch
Error prone, time demanding, tedious
2. Use SDK example
Works out of box
Difficult to modify
3. Use config tools
Easy to use and modify
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Application LED using SDK example
LED using the SDK example
Select Import SDK example(s)...
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Application LED using SDK example
1. Open the K6x
2. Select the MK66FN2M0xxx18
3. Click the board image
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Application LED using SDK example
1. Open driver_examples →
gpio
2. Select the
gpio_led_output
example
3. Click Finish
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Application LED using SDK example
Opened example project
Pins and clocks are already configured
GPIO_PinInit
GPIO_PortToggle
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Application Button using config tools
Button control program
We will show you how to check for button presses
The end goal is to write program which will print text to console
when SW2 is pressed
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Application Button using config tools
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Application Button using config tools
You should see the Pin tool now
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Application Button using config tools
Initialization
How configuration tools can help us:
Modify settings easily
Visual representation of configuration
Great for custom boards (generates defines for custom boards
that simplify management)
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Application Button using config tools
Configuration
Pins tool contains predefined configurations
We should already see the red LED configured
Add the configuration for SW2 and SW3 buttons
Search for SW2 and SW3 on the “pins” window
Click on the checkboxes for SW2 and SW3 and add the GPIO
option
This will call initialization code for the button pins on program
startup
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Application Button using config tools
Code preview was updated
If you check the Code Preview tab, you should see that the
pin_mux.c file now has extra SW2 and SW3 configuration
You should see in the Routed Pins tab (lower-left corner) that
button pins are routed to PTD11 (SW2) and PTA10 (SW3)
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Application Button using config tools
Updating code
Click the Update Code button
It opens the Update Files dialog
You can check which changes will be made
For now, just click OK
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Application Button using config tools
Writing actual code
Task - Reading a button and printing to console
Read the current state of the GPIO Button (SW2 and/or SW3)
If button is pressed, print text to console
Otherwise, do nothing
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Application Button using config tools
Issues
When you press the button, text is printed several times
Why?
What are the ways to resolve it?
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Application Button using config tools
Work Progress
Write an application that toggles green LED when SW3 is
pressed
Fix the issue with the button press being registered more than
once
Make the LED change color every time it is turned on
There are three controllable LEDs on the board
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Homework
Homework
Write an application which reacts to both buttons
SW2 button press selects color
SW3 button press toggles the color on and off
All colors start turned off
Selected color starts on red
Colors switch in the following order: Red → Green → Blue →
Red...
Application must be immune to the effects of bouncing
SW3 SW2 SW3 SW3
Red on Green selected Green on Green off
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Homework
Submission
Git tag - “Submission_02_x”
One project per branch!
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