For further power savings the PIOSC can be disabled through the
PIOSCPD
bit in the
DSCLKCFG
register. When the Deep-Sleep exit event occurs, hardware brings the system clock back to the
source and frequency it had at the onset of Deep-Sleep mode before enabling the clocks that had
been stopped during the Deep-Sleep duration. If the PIOSC is used as the PLL reference clock
source, it may continue to provide the clock during Deep-Sleep. See page 281.
Note:
If the MOSC is chosen as the Deep-Sleep clock source in the
DSCLKCFG
register, the
MOSC must also be configured as the Run and Sleep clock source in the
RSCLKCFG
register prior to entering Deep Sleep. If the PIOSC, LFIOSC, or Hibernation RTC Module
Oscillator (HIBLFIOSC or 32-kHz crystal) is configured as the Run and Sleep clock source
in the
RSCLKFCFG
register, and the MOSC is configured as the Deep-Sleep clock source
in the
DSCLKCFG
register, then two outcomes are possible:
■ If the PIOSC is still powered in Deep Sleep (using the
PIOSCPD
bit in the
DSCLKCFG
register) then the PIOSC is utilized as the clock source when entering Deep Sleep and
the device enters and exits the Deep-Sleep state normally. The MOSC is not used as
the clock source in Deep Sleep.
■ If the PIOSC has been configured to be powered down in Deep Sleep, then the device
can enter the Deep-Sleep state, but cannot exit properly. This situation can be avoided
by programming the MOSC as the Run and Sleep clock source in the
RSCLKCFG
register prior to entering Deep Sleep.
To provide the lowest possible Deep-Sleep power consumption as well the ability to wake the
processor from a peripheral without reconfiguring the peripheral for a change in clock, some of the
communications modules have a Clock Control register at offset 0xFC8 in the module register space.
The
CS
field in the Clock Control register allows the user to select the PIOSC or ALTCLK as the
clock source for the module's baud clock. When the microcontroller enters Deep-Sleep mode, the
PIOSC or ALTCLK becomes the source for the module clock as well, which allows the transmit and
receive FIFOs to continue operation while the part is in Deep-Sleep. Figure 5-6 on page 242 shows
how the clocks are selected.
241
June 18, 2014
Texas Instruments-Production Data
Tiva
™
TM4C1294NCPDT Microcontroller