LM3S1651 Datasheet, PDF (475/1033 Pages) Texas Instruments – ARM and Thumb are registered trademarks and Cortex is a trademark

Stellaris^® LM3S1651 Microcontroller
10.4.4
3. In the GPTM Timer Mode (GPTMTnMR) register, write the TnCMR field to 0x0 and the TnMR
field to 0x3.
4. Configure the type of event(s) that the timer captures by writing the TnEVENT field of the GPTM
Control (GPTMCTL) register.
5. If a prescaler is to be used, write the prescale value to the GPTM Timer n Prescale Register
(GPTMTnPR).
6. Load the timer start value into the GPTM Timer n Interval Load (GPTMTnILR) register.
7. Load the event count into the GPTM Timer n Match (GPTMTnMATCHR) register.
8. If interrupts are required, set the CnMIM bit in the GPTM Interrupt Mask (GPTMIMR) register.
9. Set the TnEN bit in the GPTMCTL register to enable the timer and begin waiting for edge events.
10. Poll the CnMRIS bit in 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 CnMCINT bit of the GPTM
Interrupt Clear (GPTMICR) register.
When counting down in Input Edge-Count Mode, the timer stops after the programmed number of
edge events has been detected. To re-enable the timer, ensure that the TnEN bit is cleared and
repeat #4 on page 475 through #9 on page 475.
Input Edge Timing Mode
A timer is configured to Input Edge Timing mode by the following sequence:
1. Ensure the timer is disabled (the TnEN bit is cleared) before making any changes.
2. Write the GPTM Configuration (GPTMCFG) register with a value of 0x0000.0004.
3. In the GPTM Timer Mode (GPTMTnMR) register, write the TnCMR field to 0x1 and the TnMR
field to 0x3.
4. Configure the type of event that the timer captures by writing the TnEVENT field of the GPTM
Control (GPTMCTL) register.
5. Load the timer start value into the GPTM Timer n Interval Load (GPTMTnILR) register.
6. If interrupts are required, set the CnEIM bit in the GPTM Interrupt Mask (GPTMIMR) register.
7. Set the TnEN bit in the GPTM Control (GPTMCTL) register to enable the timer and start counting.
8. Poll the CnERIS bit in 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 CnECINT bit of the GPTM
Interrupt Clear (GPTMICR) register. The time at which the event happened can be obtained
by reading the GPTM Timer n (GPTMTnR) register.
In Input Edge Timing mode, the timer continues running after an edge event has been detected,
but the timer interval can be changed at any time by writing the GPTMTnILR register. The change
takes effect at the next cycle after the write.
January 21, 2012
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