LM3S3749 Luminary Micro, Inc, LM3S3749 Datasheet - Page 299

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

11.2.1
11.2.2
11.2.2.1 32-Bit One-Shot/Periodic Timer Mode
June 02, 2008
GPTM Reset Conditions
After reset has been applied to the GPTM module, the module is in an inactive state, and all control
registers are cleared and in their default states. Counters TimerA and TimerB are initialized to
0xFFFF, along with their corresponding load registers: the GPTM TimerA Interval Load
(GPTMTAILR) register (see page 323) and the GPTM TimerB Interval Load (GPTMTBILR) register
(see page 324). The prescale counters are initialized to 0x00: the GPTM TimerA Prescale
(GPTMTAPR) register (see page 327) and the GPTM TimerB Prescale (GPTMTBPR) register (see
page 328).
32-Bit Timer Operating Modes
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 310), 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 314), 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 triggers when it reaches
the 0x000.0000 state. The GPTM sets the TATORIS bit in the GPTM Raw Interrupt Status
(GPTMRIS) register (see page 319), and holds it until it is cleared by writing the GPTM Interrupt
Clear (GPTMICR) register (see page 321). If the time-out interrupt is enabled in the GPTM Interrupt
Mask (GPTIMR) register (see page 317), the GPTM also sets the TATOMIS bit in the GPTM Masked
Interrupt Status (GPTMMIS) register (see page 320). The trigger is enabled by setting the TAOTE
bit in GPTMCTL, and can trigger SoC-level events such as ADC conversions.
GPTM TimerA Interval Load (GPTMTAILR) register [15:0], see page 323
GPTM TimerB Interval Load (GPTMTBILR) register [15:0], see page 324
GPTM TimerA (GPTMTAR) register [15:0], see page 329
GPTM TimerB (GPTMTBR) register [15:0], see page 330
Preliminary
LM3S3749 Microcontroller
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