LM3S308 Luminary Micro, Inc, LM3S308 Datasheet - Page 129

• Manufacturer Part Number: LM3S308
• Description: Lm3s308 Arm Microcontroller
• Manufacturer: Luminary Micro, Inc

8.1.3
8.1.4
8.1.5
8.2
Table 8-1. GPIO Pad Configuration Examples
June 04, 2008
Configuration
Digital Input (GPIO)
Digital Output (GPIO)
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 141).
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 142), 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.
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.
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.
Initialization and Configuration
To use the GPIO, the peripheral clock must be enabled by setting the appropriate GPIO Port bit
field (GPIOn) in the RCGC2 register.
On reset, all GPIO pins (except for the five JTAG pins) default to general-purpose input mode
(GPIODIR=0 and GPIOAFSEL=0). Table 8-1 on page 129 shows all possible configurations of the
GPIO pads and the control register settings required to achieve them. Table 8-2 on page 130 shows
how a rising edge interrupt would be configured for pin 2 of a GPIO port.
GPIO Register Bit Value
AFSEL
0
0
DIR
0
1
ODR
a
0
0
DEN
Preliminary
1
1
PUR
?
?
PDR
?
?
DR2R
X
?
DR4R
LM3S308 Microcontroller
X
?
DR8R
X
?
SLR
X
?
129