LM3S5R36_13 Datasheet, PDF (294/1063 Pages) Texas Instruments – LM3S5R36 Microcontroller

Hibernation Module
NRND: Not recommended for new designs.
6.4
6.4.1
Initialization and Configuration
The Hibernation module has several different configurations. The following sections show the
recommended programming sequence for various scenarios. The examples below assume that a
32.768-kHz oscillator is used, and thus always set the CLKSEL bit of the HIBCTL register. If a
4.194304-MHz crystal is used instead, then the CLKSEL bit remains cleared. Because the Hibernation
module runs at 32.768 kHz and is asynchronous to the rest of the microcontroller, which is run off
the system clock, software must allow a delay of t_{HIB_REG_ACCESS} after writes to certain registers
(see “Register Access Timing” on page 289). The registers that require a delay are listed in a note
in “Register Map” on page 296 as well as in each register description.
Initialization
The Hibernation module comes out of reset with the system clock enabled to the module, but if the
system clock to the module has been disabled, then it must be re-enabled, even if the RTC feature
is not used. See page 257.
If a 4.194304-MHz crystal is used as the Hibernation module clock source, perform the following
step:
1. Write 0x40 to the HIBCTL register at offset 0x10 to enable the crystal and select the divide-by-128
input path.
If a 32.678-kHz single-ended oscillator is used as the Hibernation module clock source, then perform
the following steps:
1. Write 0x44 to the HIBCTL register at offset 0x10 to enable the oscillator input and bypass the
on-chip oscillator.
2. No delay is necessary.
The above steps are only necessary when the entire system is initialized for the first time. If the
microcontroller has been in hibernation, then the Hibernation module has already been powered
up and the above steps are not necessary. The software can detect that the Hibernation module
and clock are already powered by examining the CLK32EN bit of the HIBCTL register.
Table 6-2 on page 294 illustrates how the clocks function with various bit setting both in normal
operation and in hibernation.
Table 6-2. Hibernation Module Clock Operation
CLK32EN PINWEN RTCWEN CLKSEL RTCEN Result Normal Operation
Result Hibernation
0
X
X
X
X Hibernation module disabled
Hibernation module disabled
1
0
0
0
1 RTC match capability enabled. No hibernation
Module clocked from
4.184304-MHz crystal.
1
0
0
1
1 RTC match capability enabled. No hibernation
Module clocked from 32.768-kHz
oscillator.
1
0
1
X
1 Module clocked from selected RTC match for wake-up event
source
1
1
0
X
0 Module clocked from selected Clock is powered down during
source
hibernation and powered up again
on external wake-up event.
294
October 06, 2012
Texas Instruments-Production Data