LM3S610 Data Sheet
October 8, 2006 111
Preliminary
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 (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 Se lect (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 GPIO Interrupt Clear (GPIOICR) regis te r (see
page 123).
When programming interrupts, 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.
8.2.4 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 124), 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.
8.2.5 Pad Configuration
The pad configuration registers allow for GPIO pad configuration by software based on the
application requirements. The pad configuration registers include the GPIODR2R, GPIODR4R,
GPIODR8R, GPIOODR, GPIOPUR, GPIOPDR, GPIOSLR, and GPIODEN registers.
8.2.6 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.
8.3 Initialization and Configuration
To use the GPIO, the peripheral clock must be enabled by setting PORTA, PORTB, PORTC, PORTD,
and PORTE in the RCGC2 register.
On reset, all GPIO pins (except for the five JTAG pins) default to general-purpose input mode
(GPIODIR and GPIOAFSEL both set to 0). Table 8-1 shows all possible configurations of the
