LM3S5G31 Datasheet, PDF (428/1223 Pages) Texas Instruments – Stellaris LM3S5G31 Microcontroller

General-Purpose Input/Outputs (GPIOs)
page 453) are not committed to storage unless the GPIO Lock (GPIOLOCK) register (see page 455)
has been unlocked and the appropriate bits of the GPIO Commit (GPIOCR) register (see page 456)
have been set.
9.2.5
Pad Control
The pad control registers allow software to configure the GPIO pads based on the application
requirements. The pad control registers include the GPIODR2R, GPIODR4R, GPIODR8R, GPIOODR,
GPIOPUR, GPIOPDR, GPIOSLR, and GPIODEN registers. These registers control drive strength,
open-drain configuration, pull-up and pull-down resistors, slew-rate control and digital input enable
for each GPIO.
9.2.6
Identification
The identification registers configured at reset allow software to detect and identify the module as
a GPIO block. The identification registers include the GPIOPeriphID0-GPIOPeriphID7 registers as
well as the GPIOPCellID0-GPIOPCellID3 registers.
9.3 Initialization and Configuration
The GPIO modules may be accessed via two different memory apertures. The legacy aperture, the
Advanced Peripheral Bus (APB), is backwards-compatible with previous Stellaris parts. The other
aperture, the Advanced High-Performance Bus (AHB), offers the same register map but provides
better back-to-back access performance than the APB bus. These apertures are mutually exclusive.
The aperture enabled for a given GPIO port is controlled by the appropriate bit in the GPIOHBCTL
register (see page 220).
To use the pins in a particular GPIO port, the clock for the port must be enabled by setting the
appropriate GPIO Port bit field (GPIOn) in the RCGC2 register (see page 273).
When the internal POR signal is asserted and until otherwise configured, all GPIO pins are configured
to be undriven (tristate): GPIOAFSEL=0, GPIODEN=0, GPIOPDR=0, and GPIOPUR=0, except for
the pins shown in Table 9-1 on page 420. Table 9-4 on page 428 shows all possible configurations
of the GPIO pads and the control register settings required to achieve them. Table 9-5 on page 429
shows how a rising edge interrupt is configured for pin 2 of a GPIO port.
Table 9-4. GPIO Pad Configuration Examples
Configuration
GPIO Register Bit Value^a
AFSEL DIR
ODR
DEN
Digital Input (GPIO)
0
0
0
1
Digital Output (GPIO)
0
1
0
1
Open Drain Output
0
1
1
1
(GPIO)
Open Drain
1
X
1
1
Input/Output (I²C)
Digital Input (Timer
1
X
0
1
CCP)
Digital Input (QEI)
1
X
0
1
Digital Output (PWM)
1
X
0
1
Digital Output (Timer
1
X
0
1
PWM)
Digital Input/Output
1
X
0
1
(SSI)
PUR
?
?
X
X
?
?
?
?
?
PDR
?
?
X
X
?
?
?
?
?
DR2R
X
?
?
?
X
X
?
?
?
DR4R
X
?
?
?
X
X
?
?
?
DR8R
X
?
?
?
X
X
?
?
?
SLR
X
?
?
?
X
X
?
?
?
428
July 03, 2014
Texas Instruments-Production Data