TM4C1236H6PM Datasheet, PDF (219/1236 Pages) Texas Instruments – Tiva Microcontroller

Tiva^™ TM4C1236H6PM Microcontroller
5.2.6.2
5.2.6.3
Sleep Mode
In Sleep mode, the clock frequency of the active peripherals is unchanged, but the processor and
the memory subsystem are not clocked and therefore no longer execute code. Sleep mode is entered
by the Cortex-M4F core executing a WFI (Wait for Interrupt) instruction. Any properly configured
interrupt event in the system brings the processor back into Run mode. See “Power
Management” on page 106 for more details.
Peripherals are clocked that are enabled in the peripheral-specific SCGC registers when auto-clock
gating is enabled (see the RCC register) or the peripheral-specific RCGC registers when the
auto-clock gating is disabled. The system clock has the same source and frequency as that during
Run mode.
Additional sleep modes are available that lower the power consumption of the SRAM and Flash
memory. However, the lower power consumption modes have slower sleep and wake-up times,
see “Dynamic Power Management” on page 220 for more information.
Important: Before executing the WFI instruction, software must confirm that the EEPROM is not
busy by checking to see that the WORKING bit in the EEPROM Done Status (EEDONE)
register is clear.
Deep-Sleep Mode
In Deep-Sleep mode, the clock frequency of the active peripherals may change (depending on the
Deep-Sleep mode clock configuration) in addition to the processor clock being stopped. An interrupt
returns the microcontroller to Run mode from one of the sleep modes; the sleep modes are entered
on request from the code. Deep-Sleep mode is entered by first setting the SLEEPDEEP bit in the
System Control (SYSCTRL) register (see page 158) and then executing a WFI instruction. Any
properly configured interrupt event in the system brings the processor back into Run mode. See
“Power Management” on page 106 for more details.
The Cortex-M4F processor core and the memory subsystem are not clocked in Deep-Sleep mode.
Peripherals are clocked that are enabled in the peripheral-specific DCGC registers when auto-clock
gating is enabled (see the RCC register) or the peripheral-specific RCGC registers when auto-clock
gating is disabled. The system clock source is specified in the DSLPCLKCFG register. When the
DSLPCLKCFG register is used, the internal oscillator source is powered up, if necessary, and other
clocks are powered down. If the PLL is running at the time of the WFI instruction, hardware powers
the PLL down and overrides the SYSDIV field of the active RCC/RCC2 register, to be determined
by the DSDIVORIDE setting in the DSLPCLKCFG register, up to /16 or /64 respectively. USB PLL
is not powered down by execution of WFI instruction. 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 254.
Important: Before executing the WFI instruction, software must confirm that the EEPROM is not
busy by checking to see that the WORKING bit in the EEPROM Done Status (EEDONE)
register is clear.
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 as the clock source
for the module's baud clock. When the microcontroller enters Deep-Sleep mode, the PIOSC becomes
June 12, 2014
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