LM3S1N16 Datasheet, PDF (447/794 Pages) Texas Instruments – Stellaris® LM3S1N16 Microcontroller

Stellaris^® LM3S1N16 Microcontroller
10.4.1
10.4.2
This section shows module initialization and configuration examples for each of the supported timer
modes.
One-Shot/Periodic Timer Mode
The GPTM is configured for One-Shot and Periodic modes by the following sequence:
1. Ensure the timer is disabled (the TnEN bit in the GPTMCTL register is cleared) before making
any changes.
2. Write the GPTM Configuration Register (GPTMCFG) with a value of 0x0000.0000.
3. Configure the TnMR field in the GPTM Timer n Mode Register (GPTMTnMR):
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. Load the start value into the GPTM Timer n Interval Load Register (GPTMTnILR).
6. If interrupts are required, set the appropriate bits in the GPTM Interrupt Mask Register
(GPTMIMR).
7. Set the TnEN bit in the GPTMCTL register to enable the timer and start counting.
8. Poll the GPTMRIS register or wait for the interrupt to be generated (if enabled). In both cases,
the status flags are cleared by writing a 1 to the appropriate bit of the GPTM Interrupt Clear
Register (GPTMICR).
If the TnMIE bit in the GPTMTnMR 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.
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 n Match Register (GPTMTnMATCHR).
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.
January 21, 2012
447
Texas Instruments-Production Data