Datasheet

Table 16-8. Counter Values When the Timer is Enabled in Input Event-Count Mode
Count Up ModeCount Down ModeRegister
0x0GPTMTnILRTnR
0x0GPTMTnILRTnV
When software writes the TnEN bit in the GPTMCTL register, the timer is enabled for event capture.
When the selected input event is detected, the current timer counter value is captured in the
GPTMTnR and GPTMTnPS register and is available to be read by the microcontroller. The GPTM
then asserts the CnERIS bit in the GPTM Raw Interrupt Status (GPTMRIS) register, and holds it
until it is cleared by writing the GPTM Interrupt Clear (GPTMICR) register. If the capture mode
event interrupt is enabled in the GPTM Interrupt Mask (GPTMIMR) register, the GPTM also sets
the CnEMIS bit in the GPTM Masked Interrupt Status (GPTMMIS) register. In this mode, the
GPTMTnR and GPTMTnPS registers hold the time at which the selected input event occurred while
the GPTMTnV register holds the free-running timer value. These registers can be read to determine
the time that elapsed between the interrupt assertion and the entry into the ISR.
In addition to generating interrupts, an ADC and/or a μDMA trigger can be generated. The ADC
trigger is enabled by setting the TnOTE bit in GPTMCTL and the event that activates the ADC is
configured in the GPTM ADC Event (GPTMADCEV) register. The μDMA trigger is enabled by
configuring the appropriate μDMA channel as well as the type of trigger selected in the GPTM DMA
Event (GPTMDMAEV) register. See “Channel Configuration” on page 712.
After an event has been captured, the timer does not stop counting. It continues to count until the
TnEN bit is cleared. When the timer reaches the timeout value, it is reloaded with 0x0 in up-count
mode and the value from the GPTMTnILR and GPTMTnPR registers in down-count mode.
Figure 16-3 on page 1113 shows how input edge timing mode works. In the diagram, it is assumed
that the start value of the timer is the default value of 0xFFFF, and the timer is configured to capture
rising edge events.
Each time a rising edge event is detected, the current count value is loaded into the GPTMTnR and
GPTMTnPS registers, and is held there until another rising edge is detected (at which point the new
count value is loaded into the GPTMTnR and GPTMTnPS registers).
December 13, 20131112
Texas Instruments-Advance Information
General-Purpose Timers