GPIO Registers
1224
SLAU723A – October 2017 – Revised October 2018
Copyright © 2017–2018, Texas Instruments Incorporated
General-Purpose Input/Outputs (GPIOs)
17.5.18 GPIODEN Register (Offset = 0x51C) [reset = X]
GPIO Digital Enable (GPIODEN)
NOTE:
Pins configured as digital inputs are Schmitt-triggered.
The GPIODEN register is the digital enable register. By default, all GPIO signals except those listed below
are configured out of reset to be undriven (tristate). Their digital function is disabled; they do not drive a
logic value on the pin and they do not allow the pin voltage into the GPIO receiver. To use the pin as a
digital input or output (either GPIO or alternate function), the corresponding GPIODEN bit must be set.
The table below shows special consideration GPIO pins. Most GPIO pins are configured as GPIOs and
high-impedance by default (GPIOAFSEL = 0, GPIODEN = 0, GPIOPDR = 0, GPIOPUR = 0, and
GPIOPCTL = 0). Special consideration pins may be programed to a nonGPIO function or may have
special commit controls out of reset. In addition, a Power-On-Reset (POR) returns these GPIO to their
original special consideration state.
The reset value for this register is 0x00000000 for GPIO ports that are not listed in
.
(1)
This pin is configured as a GPIO by default but is locked and can only be reprogrammed by unlocking the pin in the GPIOLOCK
register and uncommitting it by setting the GPIOCR register.
Table 17-27. GPIO Pins With Special Considerations
GPIO Pins
Default Reset
State
GPIOAFSEL
GPIODEN
GPIOPDR
GPIOPUR
GPIOPCTL
GPIOCR
PC[3:0]
JTAG/SWD
1
1
0
1
0x1
0
PD[7]
GPIO
(1)
0
0
0
0
0x0
0
PE[7]
GPIO
(1)
0
0
0
0
0x0
0
The GPIO commit control registers provide a layer of protection against accidental programming of critical
hardware signals including the GPIO pins that can function as JTAG/SWD signals and the NMI signal. The
commit control process must be followed for these pins, even if they are programmed as alternate
functions other than JTAG/SWD or NMI; see
NOTE:
If the device fails initialization during reset, the hardware toggles the TDO output as an
indication of failure. Thus, during board layout, designers should not designate the TDO pin
as a GPIO in sensitive applications where the possibility of toggling could affect the design.
NOTE:
The GPIO commit control registers provide a layer of protection against accidental
programming of critical hardware peripherals. Protection is provided for the GPIO pins that
can be used as the four JTAG/SWD pins and the NMI pin (see for pin numbers). Writes to
protected bits of the GPIO Alternate Function Select (GPIOAFSEL) register (see
), GPIO Pullup Select (GPIOPUR) register (see
), GPIO
Pulldown Select (GPIOPDR) register (see
), and GPIO Digital Enable
(GPIODEN) register (see
) are not committed to storage unless the GPIO
Lock (GPIOLOCK) register (see
) has been unlocked and the appropriate bits
of the GPIO Commit (GPIOCR) register (see
) have been set.