LM3S1911-IRN20-A0T Luminary Micro, Inc., LM3S1911-IRN20-A0T Datasheet - Page 195

• Manufacturer Part Number: LM3S1911-IRN20-A0T
• Description: Microcontroller
• Manufacturer: Luminary Micro, Inc.

10.2.2.1 32-Bit One-Shot/Periodic Timer Mode
10.2.2.2 32-Bit Real-Time Clock Timer Mode
October 09, 2007
This section describes the three GPTM 32-bit timer modes (One-Shot, Periodic, and RTC) and their
configuration.
The GPTM is placed into 32-bit mode by writing a 0 (One-Shot/Periodic 32-bit timer mode) or a 1
(RTC mode) to the GPTM Configuration (GPTMCFG) register. In both configurations, certain GPTM
registers are concatenated to form pseudo 32-bit registers. These registers include:
■
■
■
■
In the 32-bit modes, the GPTM translates a 32-bit write access to GPTMTAILR into a write access
to both GPTMTAILR and GPTMTBILR. The resulting word ordering for such a write operation is:
GPTMTBILR[15:0]:GPTMTAILR[15:0]
Likewise, a read access to GPTMTAR returns the value:
GPTMTBR[15:0]:GPTMTAR[15:0]
In 32-bit one-shot and periodic timer modes, the concatenated versions of the TimerA and TimerB
registers are configured as a 32-bit down-counter. The selection of one-shot or periodic mode is
determined by the value written to the TAMR field of the GPTM TimerA Mode (GPTMTAMR) register
(see page 206), and there is no need to write to the GPTM TimerB Mode (GPTMTBMR) register.
When software writes the TAEN bit in the GPTM Control (GPTMCTL) register (see page 210), the
timer begins counting down from its preloaded value. Once the 0x0000.0000 state is reached, the
timer reloads its start value from the concatenated GPTMTAILR on the next cycle. If configured to
be a one-shot timer, the timer stops counting and clears the TAEN bit in the GPTMCTL register. If
configured as a periodic timer, it continues counting.
In addition to reloading the count value, the GPTM generates interrupts and output triggers when
it reaches the 0x0000000 state. The GPTM sets the TATORIS bit in the GPTM Raw Interrupt Status
(GPTMRIS) register (see page 215), and holds it until it is cleared by writing the GPTM Interrupt
Clear (GPTMICR) register (see page 217). If the time-out interrupt is enabled in the GPTM Interrupt
Mask (GPTIMR) register (see page 213), the GPTM also sets the TATOMIS bit in the GPTM Masked
Interrupt Status (GPTMMIS) register (see page 216).
The output trigger is a one-clock-cycle pulse that is asserted when the counter hits the 0x0000.0000
state, and deasserted on the following clock cycle. It is enabled by setting the TAOTE bit in GPTMCTL.
If software reloads the GPTMTAILR register while the counter is running, the counter loads the new
value on the next clock cycle and continues counting from the new value.
If the TASTALL bit in the GPTMCTL register is asserted, the timer freezes counting until the signal
is deasserted.
In Real-Time Clock (RTC) mode, the concatenated versions of the TimerA and TimerB registers
are configured as a 32-bit up-counter. When RTC mode is selected for the first time, the counter is
GPTM TimerA Interval Load (GPTMTAILR) register [15:0], see page 219
GPTM TimerB Interval Load (GPTMTBILR) register [15:0], see page 220
GPTM TimerA (GPTMTAR) register [15:0], see page 227
GPTM TimerB (GPTMTBR) register [15:0], see page 228
Preliminary
LM3S1911 Microcontroller
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