LM3S3749 Luminary Micro, Inc, LM3S3749 Datasheet - Page 254

• Manufacturer Part Number: LM3S3749
• Description: Lm3s3749 Arm Microcontroller
• Manufacturer: Luminary Micro, Inc

General-Purpose Input/Outputs (GPIOs)
10.1.3
10.1.4
10.1.5
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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 ARM Integrated Nested Vectored
Interrupt Controller (NVIC) Interrupt Set Enable (SETNA) 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 B4, and wait for the ADC interrupt or the ADC
interrupt needs to be disabled in the SETNA register and the PortB interrupt handler polls the ADC
registers until the conversion is completed.
Interrupts are cleared by writing a 1 to the appropriate bit of the GPIO Interrupt Clear (GPIOICR)
register (see page 268).
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 269), 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.
Note:
Commit Control
The commit control registers provide a layer of protection against accidental programming of critical
hardware peripherals. Writes to protected bits of the GPIO Alternate Function Select (GPIOAFSEL)
register (see page 269), GPIO Pull-Up Select (GPIOPUR) register (see page 275), and GPIO Digital
Enable (GPIODEN) register (see page 278) are not committed to storage unless the GPIO Lock
(GPIOLOCK) register (see page 280) has been unlocked and the appropriate bits of the GPIO
Commit (GPIOCR) register (see page 281) have been set to 1.
Pad Control
The pad control registers allow for GPIO pad configuration by software 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 special high-current applications, the GPIO output buffers may be used with the following
restrictions. With the GPIO pins configured as 8-mA output drivers, a total of four GPIO outputs may
be used to sink current loads up to 18 mA each. At 18-mA sink current loading, the V
specified as 1.2 V. The high-current GPIO package pins must be selected such that there are only
a maximum of two per side of the physical package with the total number of high-current GPIO
outputs not exceeding four for the entire package.
If any pin is to be used as an ADC input, the appropriate bit in GPIOAMSEL must be written
to 1 to disable the analog isolation circuit.
Preliminary
June 02, 2008
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