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, 2014
972
Texas Instruments-Production Data
General-Purpose Timers