LM3S1969 Datasheet, PDF (289/677 Pages) Texas Instruments – Stellaris® LM3S1969 Microcontroller

OBSOLETE: TI has discontinued production of this device.
Stellaris^® LM3S1969 Microcontroller
8.2.2
8.2.3
8.2.4
Interrupt Control
The interrupt capabilities of each GPIO port are controlled by a set of seven registers. With these
registers, it is possible to select the source of the interrupt, its polarity, and the edge properties.
When one or more GPIO inputs cause an interrupt, a single interrupt output is sent to the interrupt
controller for the entire GPIO port. For edge-triggered interrupts, software must clear the interrupt
to enable any further interrupts. For a level-sensitive interrupt, it is assumed that the external source
holds the level constant for the interrupt to be recognized by the controller.
Three registers are required to define the edge or sense that causes interrupts:
■ GPIO Interrupt Sense (GPIOIS) register (see page 296)
■ GPIO Interrupt Both Edges (GPIOIBE) register (see page 297)
■ GPIO Interrupt Event (GPIOIEV) register (see page 298)
Interrupts are enabled/disabled via the GPIO Interrupt Mask (GPIOIM) register (see page 299).
When an interrupt condition occurs, the state of the interrupt signal can be viewed in two locations:
the GPIO Raw Interrupt Status (GPIORIS) and GPIO Masked Interrupt Status (GPIOMIS) registers
(see page 300 and page 301). As the name implies, the GPIOMIS register only shows interrupt
conditions that are allowed to be passed to the controller. The GPIORIS register indicates that a
GPIO pin meets the conditions for an interrupt, but has not necessarily been sent to the controller.
In addition to providing GPIO functionality, PB4 can also be used as an external trigger for the ADC.
If PB4 is configured as a non-masked interrupt pin (the appropriate bit of GPIOIM is set to 1), not
only is an interrupt for PortB generated, but an external trigger signal is sent to the ADC. If the ADC
Event Multiplexer Select (ADCEMUX) register is configured to use the external trigger, an ADC
conversion is initiated.
If no other PortB pins are being used to generate interrupts, the Interrupt 0-31 Set Enable (EN0)
register can disable the PortB interrupts, and the ADC interrupt can be used to read back the
converted data. Otherwise, the PortB interrupt handler needs to ignore and clear interrupts on PB4,
and wait for the ADC interrupt or the ADC interrupt must be disabled in the EN0 register and the
PortB interrupt handler must poll the ADC registers until the conversion is completed. See page 108
for more information.
Interrupts are cleared by writing a 1 to the appropriate bit of the GPIO Interrupt Clear (GPIOICR)
register (see page 302).
When programming the following interrupt control registers, the interrupts should be masked (GPIOIM
set to 0). Writing any value to an interrupt control register (GPIOIS, GPIOIBE, or GPIOIEV) can
generate a spurious interrupt if the corresponding bits are enabled.
Mode Control
The GPIO pins can be controlled by either hardware or software. When hardware control is enabled
via the GPIO Alternate Function Select (GPIOAFSEL) register (see page 303), the pin state is
controlled by its alternate function (that is, the peripheral). Software control corresponds to GPIO
mode, where the GPIODATA register is used to read/write the corresponding pins.
Commit Control
The GPIO commit control registers provide a layer of protection against accidental programming of
critical hardware peripherals. Protection is currently provided for the five JTAG/SWD pins (PB7 and
PC[3:0]). Writes to protected bits of the GPIO Alternate Function Select (GPIOAFSEL) register
July 24, 2012
289
Texas Instruments-Production Data