Functional Description
1259
SLAU723A – October 2017 – Revised October 2018
Copyright © 2017–2018, Texas Instruments Incorporated
General-Purpose Timers
18.3.3.1.1 Timer Compare Action Mode
The timer compare mode is an extension to the existing one-shot and periodic modes of the GPTM. This
mode can be used when an application requires a pin change state at some time in the future, regardless
of the processor state. The compare mode does not operate when the PWM mode is active and is
mutually exclusive to the PWM mode. The compare mode is enabled when the TAMR field is set to 0x1 or
0x2 (one-shot or periodic), the TnAMS bit is 0 (capture or compare mode) and the TCACT field is nonzero
in the GPTM Timer n Mode (GPTMTnMR) register. Depending on the TCACT encoding, the timer can
perform a set, clear or toggle on the corresponding CCPn pin when a timer match occurs. In 16-bit mode,
the corresponding CCP pin can have an action applied, but when operating in 32-bit mode, the action can
only be applied to the even CCP pin.
The TCACT field can be changed while the GPTM is enabled to generate different combinations of
actions. For example, during a periodic event, encodings TCACT = 0x6 or 0x7 can be used to force the
initial state of the CCPn pin before the first interrupt and following that, TCACT = 0x2 and TCACT = 0x3
can be used (alternately) to change the sense of the pin for the subsequent toggle, while possible
changing load value for the next period.
The time-out interrupts used for one-shot and periodic modes are used in the compare action modes.
Thus, the TnTORIS bits in the GPTMRIS register are triggered if the appropriate mask bits are set in the
GPTMIM register.
18.3.3.2 Real-Time Clock Timer Mode
In Real-Time Clock (RTC) mode, the concatenated versions of the Timer A and Timer B registers are
configured as an up-counter. When RTC mode is selected for the first time after reset, the counter is
loaded with a value of 0x1. All subsequent load values must be written to the GPTM Timer n Interval Load
(GPTMTnILR) registers (see
). If the GPTMTnILR register is loaded with a new value, the
counter begins counting at that value and rolls over at the fixed value of 0xFFFFFFFF.
lists the
values that are loaded into the timer registers when the timer is enabled.
Table 18-5. Counter Values When the Timer is Enabled
in RTC Mode
Register
Count Down Mode
Count Up Mode
GPTMTnR
Not available
0x1
GPTMTnV
Not available
0x1
GPTMTnPS
Not available
Not available
The input clock on a CCP 0 input must be 32.768 KHz in RTC mode. The clock signal is then divided
down to a 1-Hz rate and passed along to the input of the counter.
When software writes the TAEN bit in the GPTMCTL register, the counter starts counting up from its
preloaded value of 0x1. When the current count value matches the preloaded value in the
GPTMTnMATCHR registers, the GPTM asserts the RTCRIS bit in GPTMRIS and continues counting until
either a hardware reset, or it is disabled by software (clearing the TAEN bit). When the timer value
reaches the terminal count, the timer rolls over and continues counting up from 0x0. If the RTC interrupt is
enabled in GPTMIMR, the GPTM also sets the RTCMIS bit in GPTMMIS and generates a controller
interrupt. The status flags are cleared by writing the RTCCINT bit in GPTMICR.
In this mode, the GPTMTnR and GPTMTnV registers always have the same value.
In addition to generating interrupts, the RTC can generate a µDMA trigger. The µDMA trigger is enabled
by configuring and enabling the appropriate µDMA channel as well as the type of trigger enable in the
GPTM DMA Event (GPTMDMAEV) register (see