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.
13.4.2 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. If the timer has been operating in a different mode prior to this, clear any residual set bits in the
GPTM Timer n Mode (GPTMTnMR) register before reconfiguring.
3. Write the GPTM Configuration Register (GPTMCFG) with a value of 0x0000.0001.
4. Write the match value to the GPTM Timer n Match Register (GPTMTnMATCHR).
5. Set/clear the RTCEN and TnSTALL bit in the GPTM Control Register (GPTMCTL) as needed.
6. If interrupts are required, set the RTCIM bit in the GPTM Interrupt Mask Register (GPTMIMR).
7. Set the TAEN bit in the GPTMCTL register to enable the timer and start counting.
When the timer count equals the value in the GPTMTnMATCHR register, the GPTM asserts the
RTCRIS bit in the GPTMRIS register and continues counting until Timer A is disabled or a hardware
reset. The interrupt is cleared by writing the RTCCINT bit in the GPTMICR register. Note that if the
GPTMTnILR register is loaded with a new value, the timer begins counting at this new value and
continues until it reaches 0xFFFF.FFFF, at which point it rolls over.
13.4.3 Input Edge-Count Mode
A timer is configured to Input Edge-Count 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 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. Program registers according to count direction:
■ In down-count mode, the GPTMTnMATCHR and GPTMTnPMR registers are configured so
that the difference between the value in the GPTMTnILR and GPTMTnPR registers and the
GPTMTnMATCHR and GPTMTnPMR registers equals the number of edge events that must
be counted.
■ In up-count mode, the timer counts from 0x0 to the value in the GPTMTnMATCHR and
GPTMTnPMR registers. Note that when executing an up-count, the value of the GPTMTnPR
and GPTMTnILR must be greater than the value of GPTMTnPMR and GPTMTnMATCHR.
June 18, 2014972
Texas Instruments-Production Data
General-Purpose Timers
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