GPIOs are the basic interfaces of any microcontroller. For a positive logical system, a GPIO pin can be set high (taking the value 1) by connecting it to a voltage supply, or set low (taking the value 0) by connecting it ti ground. The Tiva LaunchPad can set the GPIO pin to take either value and treat it as an output, or it can detect the value of the pin and treat it as an input.
You will learn how to write an assembly or C code to configure the GPIO ports, read the status of switches and turn on/off the LEDs.
Required Components List
Tiva EK-TM4C123GXL LaunchPad Kit or EK-TM4C1294XL LaunchPad Kit.
The switchese and LEDs on the Tiva LaunchPads board will be used in this lab.
Circuit / Schematic Diagram
You have to know the location of LEDs and switches on the TI Tiva board.
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)
In your code, you need to configure GPIO Port F pin 0 and pin 4 as inputs; Port F pin 1, pin 2 and pin 3 as outputs.
Note: The SW1 and SW2 are directly connected with GND. Therefore, these pins are as negative logic input, you have to enable the internal resistor for these pins.
EK-TM4C1294XL LaunchPad
The EK-TM4C1294XL LaunchPad comes with fiur green LEDs and two user buttons. Table 2 shows how these features are connected to the pins on the microcontroller.
Table 2: 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
In your code, you need to initialize GPIO Port J pin 0 and pin 1 as inputs; Port F pin 0 and pin 4 as outputs.
Note: The SW1 and SW2 are directly connected with GND. Therefore, those pins are as negative logic input, you have to enable the internal resistor for those pins.
Procedure
The first important thing for this lab is the GPIO configuration. When the processor has started executing, but before you can run application software on the processor, it must be initialized, including loading the appropriate software-configuration. The "Lesson 10: GPIO Ports and Configurations"describes the detailed steps that the software must take to initialize the GPIO Ports after reset.
Creating a New Project
Launch the Keil μVision5 IDE, create a New Project, add MyDefines.h to the Source Group, and and add the Common folder to the Include Paths option.
Configurations
Write down the following configuration information into your lab report.
Next, we need to configure all the GPIO ports and pins that are used in the designd.
According to the pin connections, complete the following GPIO configurations for each port. Fills the pin field by the value below:
0: Clean the bit
1: Set the bit
x: Do not change the bit
d: Do not care
For both TM4C123GXL and TM4C1294XL LaunchPads, the Port C [3:0] are used for JTAG/SWD. Therefore, when you configure the Port C, you have to use bitwise operators to make sure your new configuration settings do not affect the JTAG/SWD function (PC3 ~ PC0).
Most of GPIO pins are configured as GPIOs and tri-stated by default (GPIOPCTL = 0, CPIOAFSEL = 0, GPIODIR = 0, GPIOPUR = 0, GPIOPDR = 0, GPIOODR = 0)
Enable Clock to the GPIO Modules (RCGCGPIO register) TM4C123G: SYSCTL->RCGCGPIO|= binary = hex
8
4
2
1
8
4
2
1
7
6
5
4
3
2
1
0
bit
Port F
Port E
Port D
Port C
Port B
Port A
port
0
0
-
TM4C1294: SYSCTL->RCGCGPIO |= binary = hex
8
4
2
1
8
4
2
1
8
4
2
1
8
4
2
1
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
bit
Port Q
Port P
Port N
Port M
Port L
Port K
Port J
Port H
Port G
Port F
Port E
Port D
Port C
Port B
Port A
port
0
-
-
-
After enable clock signal, check the PRGPIO register until the correspoding bit set to 1.
Unlock Port TM4C123G: PD7 and PF0 are locked after reset. TM4C1294: PD7 and PE7 are locked after reset If those pins are used in the design, it must be unlocked first. To unlock the port, 0x4C4F434B must be written into GPIOLOCK register and uncommit it by setting the GPIOCR register.
8
4
2
1
8
4
2
1
7
6
5
4
3
2
1
0
bit
Port
Pin 7
Pin 6
Pin 5
Pin 4
-
Pin 3
Pin 2
Pin 1
Pin 0
pin
Value in Hex
Register
Value to Register
-
-
=
➤
GPIO->LOCK
=
0x4C4F434B
-
-
=
➤
GPIO->CR
-
-
=
➤
GPIO->LOCK
=
0x4C4F434B
-
-
=
➤
GPIO->CR
Convert above configuration into registers
GPIO Analog Mode Select If any pin is used as an Analog signal (check Signal Type field on the table 1), the appropriate bit in AMSEL must be set.
0: Digital signal
1: Analog signal
8
4
2
1
8
4
2
1
7
6
5
4
3
2
1
0
bit
Port
Pin 7
Pin 6
Pin 5
Pin 4
-
Pin 3
Pin 2
Pin 1
Pin 0
pin
Value in Hex
Register
Value to Register
-
-
=
➤
GPIO->AMSEL
-
-
=
➤
GPIO->AMSEL
-
-
=
➤
GPIO->AMSEL
-
-
=
➤
GPIO->AMSEL
-
-
=
➤
GPIO->AMSEL
-
-
=
➤
GPIO->AMSEL
-
-
=
➤
GPIO->AMSEL
GPIO Port Control (PCTL) The PCTL register is used to select the specific periheral signal for each GPIO pin when using the alternate function mode.
0: GPIO
1~0xF: Check the GPIO Pins and Alternate Function table
GPIO Alternate Function Select (AFSEL) Setting a bit in AFSEL register configures the corresponding GPIO pin to be controlled by PCTL peripheral function.
0: General I/O
1: Pin connected to the digital function that defined in PCTL register
8
4
2
1
8
4
2
1
7
6
5
4
3
2
1
0
bit
Port
Pin 7
Pin 6
Pin 5
Pin 4
-
Pin 3
Pin 2
Pin 1
Pin 0
pin
Value in Hex
Register
Value to Register
-
-
=
➤
GPIO->AFSEL
-
-
=
➤
GPIO->AFSEL
-
-
=
➤
GPIO->AFSEL
-
-
=
➤
GPIO->AFSEL
-
-
=
➤
GPIO->AFSEL
-
-
=
➤
GPIO->AFSEL
-
-
=
➤
GPIO->AFSEL
GPIO Pin Direction (DIR) Set pin direction
0: Input pin
1: Output pin
8
4
2
1
8
4
2
1
7
6
5
4
3
2
1
0
bit
Port
Pin 7
Pin 6
Pin 5
Pin 4
-
Pin 3
Pin 2
Pin 1
Pin 0
pin
Value in Hex
Register
Value to Register
-
-
=
➤
GPIO->DIR
-
-
=
➤
GPIO->DIR
-
-
=
➤
GPIO->DIR
-
-
=
➤
GPIO->DIR
-
-
=
➤
GPIO->DIR
-
-
=
➤
GPIO->DIR
-
-
=
➤
GPIO->DIR
Internal Pull-Up Resistor (PUR), Pull-Down Resistor (PDR), and Open-Drain (ODR) PUR: The pull-up control register PDR: The pull-down control register ODR: The open-drain control register
0: Disable
1: Enable
8
4
2
1
8
4
2
1
7
6
5
4
3
2
1
0
bit
Port
Pin 7
Pin 6
Pin 5
Pin 4
-
Pin 3
Pin 2
Pin 1
Pin 0
pin
Value in Hex
Register
Value to Register
-
-
=
➤
GPIO->
-
-
=
➤
GPIO->
-
-
=
➤
GPIO->
-
-
=
➤
GPIO->
-
-
=
➤
GPIO->
-
-
=
➤
GPIO->
-
-
=
➤
GPIO->
GPIO Digital Enable Enables all the pins that are used in the design, including GPIO pins and alternate function pins.
0: Pin undriven
1: Enable pin
8
4
2
1
8
4
2
1
7
6
5
4
3
2
1
0
bit
Port
Pin 7
Pin 6
Pin 5
Pin 4
-
Pin 3
Pin 2
Pin 1
Pin 0
pin
Value in Hex
Register
Value to Register
-
-
=
➤
GPIO->DEN
-
-
=
➤
GPIO->DEN
-
-
=
➤
GPIO->DEN
-
-
=
➤
GPIO->DEN
-
-
=
➤
GPIO->DEN
-
-
=
➤
GPIO->DEN
-
-
=
➤
GPIO->DEN
Lab Experiment
After the GPIO configuration, use the polling method to check the SW1 status, and then check SW2 status as shown on the following diagram.
Figure: Flowchart Diagram
For EK-TM4C123GXL Board:
Press SW1 (PF4) to turn on Red LED (PF1) for about 2 sec, then turn it off
Press SW2 (PF0) to turn on Green LED (PF3) for about 2 sec, then turn it off
For EK-TM4C1294XL Board:
Press SW1 (PJ0) to turn on LED1 (PN1) for about 2 sec, then turn it off
Press SW2 (PJ1) to turn on LED2 (PN0) for about 2 sec, then turn it off
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <stdbool.h>
#include "TM4C123GH6PM.h"
#include "MyDefines.h"
void DelayMs(int ms); // Software Delay Function
void Setup_GPIO(void);
int main()
{
// Place your initialization/startup code here (e.g. Setup_GPIO() )
Setup_GPIO();
while (1) {
// Place your application code here
if ( (GPIOF->DATA & _BIT4) == false ) { // SW1 is pressed
GPIOF->DATA |= _BIT1; // Set PF1 to 1, turn on LED
DelayMs(2000);
GPIOF->DATA &= ~_BIT1; // Clear PF1 to 0, turn off LED
}
if ( !(GPIOF->DATA & _BIT0)) { // SW2 is pressed
GPIOF->DATA |= _BIT3; // Set PF3 to 1, turn on LED
DelayMs(2000);
GPIOF->DATA &= ~_BIT3; // Clear PF3 to 0, turn off LED
}
DelayMs(20);
}
}
//------------------------------------------------------------------------------
void Setup_GPIO(void)
{
// Configure GPIOs
// 1. Enable Clock to the GPIO Modules (SYSCTL->RCGCGPIO)
SYSCTL->RCGCGPIO |= ( );
// allow time for clock to stabilize (SYSCTL-PRGPIO)
while ((SYSCTL->PRGPIO & ( )) != ( )) {};
// 2. Unlock GPIO only PD7, PF0 on TM4C123G; PD7, PE7 on TM4C1294 (GPIO->LOCK and GPIO->CR
GPIOF->LOCK = 0x4C4F434B; // Unlock for GPIOF
GPIOF->CR |= _PIN0; // Commit for PIN0
// 3. Set Analog Mode Select bits for each Port (GPIO->AMSEL 0=digital, 1=analog)
// 4. Set Port Control Register for each Port (GPIO->PCTL, check the PCTL table)
// 5. Set Alternate Function Select bits for each Port (GPIO->AFSEL 0=regular I/O, 1=PCTL peripheral)
// 6. Set Output pins for each Port (Direction of the Pins: GPIO->DIR 0=input, 1=output)
// 7. Set PUR bits (internal Pull-Up Resistor), PDR (Pull-Down Resistor), ODR (Open Drain) for each Port (0: disable, 1=enable)
// 8. Set Digital ENable register on all GPIO pins (GPIO->DEN 0=disable, 1=enable)
}
//------------------------------------------------------------------------------
// Delay ms milliseconds (4167:50MHz TM4C123G CPU, 1605:16MHz TM4C123G CPU Clock)
void DelayMs(int ms)
{
volatile int i, j;
for (i = 0; i < ms; i++)
for (j = 0; j < 4167; j++) {} // Do nothing for 1ms
}
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <stdbool.h>
#include "TM4C1294NCPDT.h"
#include "MyDefines.h"
void DelayMs(int ms); // Software Delay Function
void Setup_GPIO(void);
int main()
{
// Place your initialization/startup code here (e.g. Setup_GPIO() )
Setup_GPIO();
while (1) {
// Place your application code here
if ( (GPIOJ_AHB->DATA & _BIT0) == false ) { // SW1 is pressed
GPION->DATA |= _BIT1; // Set PN1 to 1, turn on LED
DelayMs(2000);
GPION->DATA &= ~_BIT1; // Clear PN1 to 0, turn off LED
}
if ( (GPIOJ_AHB->DATA & _BIT1) == false ) { // SW2 is pressed
GPION->DATA |= _BIT0; // Set PN0 to 1, turn on LED
DelayMs(2000);
GPION->DATA &= ~_BIT0; // Clear PN0 to 0, turn off LED
}
DelayMs(20);
}
}
//------------------------------------------------------------------------------
void Setup_GPIO(void)
{
// Configure GPIOs
// 1. Enable Clock to the GPIO Modules (SYSCTL->RCGCGPIO)
SYSCTL->RCGCGPIO |= ( );
// allow time for clock to stabilize (SYSCTL-PRGPIO)
while ((SYSCTL->PRGPIO & ( )) != ( )) {};
// 2. Unlock GPIO only PD7, PF0 on TM4C123G; PD7, PE7 on TM4C1294 (GPIO->LOCK and GPIO->CR)
// 3. Set Analog Mode Select bits for each Port (GPIO->AMSEL 0=digital, 1=analog)
// 4. Set Port Control Register for each Port (GPIO->PCTL, check the PCTL table)
// 5. Set Alternate Function Select bits for each Port (GPIO->AFSEL 0=regular I/O, 1=PCTL peripheral)
// 6. Set Output pins for each Port (Direction of the Pins: GPIO->DIR 0=input, 1=output)
// 7. Set PUR bits (internal Pull-Up Resistor), PDR (Pull-Down Resistor), ODR (Open Drain) for each Port (0: disable, 1=enable)
// 8. Set Digital ENable register on all GPIO pins (GPIO->DEN 0=disable, 1=enable)
}
//------------------------------------------------------------------------------
// Delay ms milliseconds (1605: 16MHz TM4C1294 CPU Clock)
void DelayMs(int ms)
{
volatile int i, j;
for (i = 0; i < ms; i++)
for (j = 0; j < 1605; j++) {} // // Do nothing for 1ms
}
Show your result to the instructor.
Questions
When you hold down SW1 and SW2 simultaneously for a while (ex. more than 10 seconds), what happens on the LEDs?
Exercises
Using the following schematic diagram in Exercises. (For TM4C123G and TM4C1294 LaunchPad)
All LEDs must be turned off after reset (or power up),
Design a system that toggles the LEDs each time the SW is pressed.
Press SW1 to turn on LED1; If SW1 is pressed again, then turn off LED1.
Press SW2 to turn on LED2; If SW2 is pressed again, then turn off LED2.
You need to write the code to detect the signal edge that is on the falling edge.
In your code, each switch requires two variables to store the previous and current state.
Reads the SW value and saves it to the current state variable.
Check the previous and current state variables: If the previous state is a logic 1 (which means the SW button was released before) and the current state is a logic 0 (the SW button is pressed just now), this means that the falling edge occurs at the SW signal (user just pressed the SW), and then change the LED state
Stores the current state value to the previous state variable.
Questions:
After reset, you press SW1 and SW2 at the same time for 2 seconds. What are the status on the LEDs?
Release both switches, and press SW2 again. What are the status on the LEDs?
Show your result to the instructor, then submit your main.c file and flowchart diagram in the report.
