GPIO Initialization Configuration
Next, we need to configure all the GPIO ports and pins that are used in the design.
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 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 |= (_PORTs); |= 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 |= (_PORTs); |= binary = hex
After enabling the clock signal, check the PRGPIO register until the corresponding bit is set to 1.8 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 - - -
In Assembly:
LDR R0, =SYSCTL_PRGPIO_R Wait4GPIO LDR R1, [R0] TST R1, #(__) BEQ Wait4GPIOIn c:
while ( (SYSCTL->PRGPIO & ____ ) != ____ ) {}; - 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, they must be unlocked first. To unlock the port, 0x4C4F434B must be written into the 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 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 peripheral signal for each GPIO pin when using the alternate function mode.
- 0: GPIO
- 1~0xF: Check the GPIO Pins and Alternate Function table
8421 8421 8421 8421 8421 8421 8421 8421 31~28 27~24 23~20 19~16 15~12 11~8 7~4 3~0 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 ->PCTL - - = ➤ GPIO ->PCTL - - = ➤ GPIO ->PCTL - - = ➤ GPIO ->PCTL - - = ➤ GPIO ->PCTL - - = ➤ GPIO ->PCTL - - = ➤ GPIO ->PCTL - GPIO Alternate Function Select (AFSEL)
Setting a bit in the 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 defined in the 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