Tiva Lab 01: Blinking LEDs
Objectives
- Learn how to create a new C project using Keil lDE for TI Tiva LaunchPad Boards
- Learn how to use #define statements to simplify or clarify the code
- Learn how to config the GPIO for simple output pins
- Learn how to use bit-wise operators to set and clean specific bits
Required Reading Material
- Lesson 07: Create an ARM C Application with Keil μVision MDK-ARM
- Lesson 09: GPIO Ports and Configurations
- Set, Clear, Toggle and Check Bit Value in C
- Polling Method in Embedded Programming
Background Information
The Tiva launchPad has rows of connectors along both sides that are used to connect to several electronic devices and plug-in 'shields' that extend its capability. The EK-TM4C123GXL LaunchPad has a single RGB LED on the board, and the EK-TM4C1294XL LaunchPad has four LEDs on the board. Those can be used on your embedded applications. When you first time connects the board to a USB plug, the onboard LEDs maybe already blink. That is because the boards are generally shipped with the Blink sketch pre-installed.
In this lab, we will reprogram the Tiva board with our Blink code and then change the rate at which it blinks.
Please follow Lesson 04: Operations and Operators to learn how to set up the Keil μVision IDE, create a new project, download and debug the code.
Circuit / Schematic Diagram
The onboard switches and LEDs for Tiva LaunchPads are as shown below:
EK-TM4C123GXL LaunchPad - Circuit
The EK-TM4C123GXL LaunchPad comes with an RGB LED and two user buttons. Table 1 shows how these features are connected to the pins on the microcontroller.
Table 1: User Switches and RGB LED Signals
| GPIO Pin | Pin Function | User Device |
| PF4 | GPIO | SW1 |
| PF0 | GPIO | SW2 |
| PF1 | GPIO | RGB LED (Red) |
| PF2 | GPIO | RGB LED (Blue) |
| PF3 | GPIO | RGB LED (Green) |
Table2: Pin Configurations for TM4C123G
| Device | Port.Pin | Signal Type | PCTL | Direction | Drive Mode |
|---|---|---|---|---|---|
In your code, you need to configure GPIO Port F pin 1 and pin 3 as outputs.
EK-TM4C1294XL LaunchPad - Circuit
The EK-TM4C1294XL LaunchPad comes with four green LEDs and two user buttons. Table 2 shows how these features are connected to the pins on the microcontroller.
Table 3: User Switches and Green LED Signals
| GPIO Pin | Pin Function | User Device |
| PJ0 | GPIO | SW1 |
| PJ1 | GPIO | SW2 |
| PN1 | GPIO | LED1 |
| PN0 | GPIO | LED2 |
| PF4 | GPIO | LED3 |
| PF0 | GPIO | LED4 |
Table4: Pin Configurations for TM4C1294
| Device | Port.Pin | Signal Type | PCTL | Direction | Drive Mode |
|---|---|---|---|---|---|
In your code, you need to initialize GPIO Port N pin 0 and pin 1 as outputs.
Procedures
In this lab, you will learn how to create a C project for the Tiva LaunchPad board and configure the GPIO ports to blink the onboard LED.
* Before doing this lab, you must first study "Lesson 07: Create an ARM C Application with Keil μVision MDK-ARM".
- Please create a new folder under the EE3450 folder and name it Lab01_BlinkingLEDs_1. Then double-click the folder you just created to jump into it.
- Launch the Keil μVisio, create a new project, and save the project as Lab01_BlinkingLEDs_1.
- Create predefined symbolic constants for the GPIO configurations.
Create MyDefines.h
Create MyDefines.h
Create the MyDefines.h file and add it to your project.
- Use Notepad++ or other text editors to add the following definitions to the file, then save the file inside the Common folder, and name it "MyDefines.h"
- Go back to the Keil main window. Right-click on the Source Group 1 and click Add Existing Files to Group 'Source Group 1'...
- In the window that opens, change the location to the Common folder, then change the file type to the Text file (*.txt; *.h; *.inc). Select MyDefines.h file, or enter the File name "MyDefines".
Click Add, and then click Close to close the window. - Now you have already added MyDefines.h file to your project.
- Add the Common folder to the Include Paths. So, the compiler will know where to find the MyDefines.h file.
Open the Option for Target window, change the tab to C/C++, and add the Common folder on the Include Paths field.
Click OK to close the Options window.
- Use Notepad++ or other text editors to add the following definitions to the file, then save the file inside the Common folder, and name it "MyDefines.h"
- Copy-paste the following code to your main.c file.
- Modify the Setup_GPIO() function based on the Pin Configuration Table (table 2 or 4) to configure the onboard switches and LEDs.
- Inside the while(1) loop, the commands first of all turn the LED pin on (high), then delay for 1000 milliseconds (1 second), then turn the LED pin off and pause for another second.
Every C code must have a main() function, which is the entry point for the system. In the main() function, the line while(1) is the most popular used in an application for embedded microcontrollers. The line while(1) creates an infinite loop that never stops executing. It executes over and over and over again unless the program is intentionally stopped or there is some condition under this loop that gets met that takes out of this infinite loop.
Why do embedded programs contain an infinite loop? While personal computers have an operating system, embedded microcontrollers generally do not. Once a program has been executed on a personal computer, it returns control to the computer's operating system when the program is finished. An embedded microcontroller, however, does not have an operating system and cannot be allowed to fall out of the program at any time. Hence, every embedded microcontroller application has an infinite loop built into it somewhere, such as the line while(1). This prevents the program from running out of things to do and doing random things that may be undesirable.
Lab Experiments
Exp #1.1: Blinking Red and Green LEDs
Now, add additional codes to blink the green LED (LED2) every second after blinking the red LED (LED1).
Build the code. If there are no errors, download the object code to the Tiva board. You should see the LED start to blink as below.
Blinking LEDs on TH4C123G Board
Blinking LEDs on TM4C1294 Board
Exp #1.2: Two LEDs Blink Simultaneously but in Different Intervals
Now, create a second project:
- Create a project folder named "Lab01_BlinkingLEDs_2" under the EE3450 folder.
- Follow the previous procedures to create a second project.
- You can copy the main.c file from the previous project.
In this experiment, the system still controls two LEDs: Both are lit up simultaneously, but each LED will blink at different intervals. The Red LED (LED1) blinks every 500 ms, and the Green LED (LED2) blinks at 1000 ms.
You might think that you just need to duplicate the same code and then modify that code to control the second LED, such as the following:
However, you will see that the Red LED (or LED1) will be lit up for 500 ms, then turned off for 500 ms. Afterward, the Green LED (or LED2) will turn on for 1000 ms and off for 1000 ms. It will repeat the same action.
The two LEDs will interact with each other; when one is active, the other is inactive. However, they do not act at the same time. This is an incorrect function design.
Read Polling Method in Embedded Programming - Same Polling Cycles, Different Delay session. Using the following pseudoscience to design the function:
Set timeLoop1, and timeLoop2 to 0
loop
if timeLoop1 is zero
toggle Red LED or LED1
set timeLoop1 value to the number of loops for 500 ms delay cycles
if timeLoop2 is zero
toggle Green LED or LED2
set timeLoop2 value to the number of loops for 1000 ms delay cycles
delay for 10 ms (each loop has 10 ms delay)
if timeLoop1 is greater than zero
decrease timeLoop1 by 1
if timeLoop2 greater than zero
decrease timeLoop2 by 1
endloop
You must create two variables in the code to store the different timer delays. To simplify the coding, we will ignore the execution time of all instructions and add a 10ms delay in the loop. If you need to delay the timer by 30ms, you must set the value of the timer to 3 to get three delay cycles (each delay cycle is 10ms).
The final results are shown below:
Questions
Read the following datasheet for the EK-TM4C123GXL or EK-TM4C1294XL board, then find the answer to the questions
- The CPU used on the Tiva board is an ARM Cortex-M4-based processor. What is the maximum operating frequency of the processor on EK-TM4C123GXL and EK-TM4C1294XL boards?
- List all external clock sources on your Tiva LaunchPad board.
- The onboard In-Circuit Debug Interface (ICDI) supports a UART communication port, which is connected to the Tiva LaunchPad. Which GPIO pins on the Tiva LaunchPad are used for UART communication?
- Each Tiva Launchpad has two microcontrollers. What is the purpose?