LM3S9B81 Datasheet, PDF (436/1155 Pages) Texas Instruments – Stellaris® LM3S9B81 Microcontroller

General-Purpose Timers
11.4.2
11.4.3
If the TAMIE bit in the GPTMTAMR register is set, the RTCRIS bit in the GPTMRIS register is set,
and the timer continues counting. In One-Shot mode, the timer stops counting after the time-out
event. To re-enable the timer, repeat the sequence. A timer configured in Periodic mode reloads
the timer and continues counting after the time-out event.
32-Bit Real-Time Clock (RTC) Mode
To use the RTC mode, the timer must have a 32.768-KHz input signal on an even CCP input. To
enable the RTC feature, follow these steps:
1. Ensure the timer is disabled (the TAEN bit is cleared) before making any changes.
2. Write the GPTM Configuration Register (GPTMCFG) with a value of 0x0000.0001.
3. Write the match value to the GPTM Timer A Match Register (GPTMTAMATCHR).
4. Set/clear the RTCEN bit in the GPTM Control Register (GPTMCTL) as needed.
5. If interrupts are required, set the RTCIM bit in the GPTM Interrupt Mask Register (GPTMIMR).
6. Set the TAEN bit in the GPTMCTL register to enable the timer and start counting.
When the timer count equals the value in the GPTMTAMATCHR register, the counter is re-loaded
with 0x0000.0000 and begins counting. If an interrupt is enabled, it does not have to be cleared.
16-Bit One-Shot/Periodic Timer Mode
A timer is configured for 16-bit One-Shot and Periodic modes by the following sequence:
1. Ensure the timer is disabled (the TnEN bit is cleared) before making any changes.
2. Write the GPTM Configuration Register (GPTMCFG) with a value of 0x0000.0004.
3. Set the TnMR field in the GPTM Timer Mode (GPTMTnMR) register:
a. Write a value of 0x1 for One-Shot mode.
b. Write a value of 0x2 for Periodic mode.
4. Optionally configure the TnSNAPS, TnWOT, TnMTE and TnCDIR bits in the GPTMTnMR register
to select whether to capture the value of the free-running timer at time-out, use an external
trigger to start counting, configure an additional trigger or interrupt, and count up or down.
5. If a prescaler is to be used, write the prescale value to the GPTM Timer n Prescale Register
(GPTMTnPR).
6. Load the start value into the GPTM Timer Interval Load Register (GPTMTnILR).
7. If interrupts are required, set the appropriate bit in the GPTM Interrupt Mask Register
(GPTMIMR).
8. Set the TnEN bit in the GPTM Control Register (GPTMCTL) to enable the timer and start
counting.
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June 29, 2010
Texas Instruments-Advance Information