LM3S1110 Luminary Micro, Inc, LM3S1110 Datasheet - Page 114

• Manufacturer Part Number: LM3S1110
• Description: Lm3s1110 Arm Microcontroller
• Manufacturer: Luminary Micro, Inc

Hibernation Module
7.2.4
7.2.5
7.2.6
114
Real-Time Clock
The Hibernation module includes a 32-bit counter that increments once per second with a proper
clock source and configuration (see “Clock Source” on page 112). The 32.768-kHz clock signal is
fed into a predivider register which counts down the 32.768-kHz clock ticks to achieve a once per
second clock rate for the RTC. The rate can be adjusted to compensate for inaccuracies in the clock
source by using the predivider trim register, HIBRTCT. This register has a nominal value of 0x7FFF,
and is used for one second out of every 64 seconds to divide the input clock. This allows the software
to make fine corrections to the clock rate by adjusting the predivider trim register up or down from
0x7FFF. The predivider trim should be adjusted up from 0x7FFF in order to slow down the RTC
rate, and down from 0x7FFF in order to speed up the RTC rate.
The Hibernation module includes two 32-bit match registers that are compared to the value of the
RTC counter. The match registers can be used to wake the processor from hibernation mode, or
to generate an interrupt to the processor if it is not in hibernation.
The RTC must be enabled with the RTCEN bit of the HIBCTL register. The value of the RTC can be
set at any time by writing to the HIBRTCLD register. The predivider trim can be adjusted by reading
and writing the HIBRTCT register. The predivider uses this register once every 64 seconds to adjust
the clock rate. The two match registers can be set by writing to the HIBRTCM0 and HIBRTCM1
registers. The RTC can be configured to generate interrupts by using the interrupt registers (see
“Interrupts and Status” on page 115).
Non-Volatile Memory
The Hibernation module contains 64 32-bit words of memory which are retained during hibernation.
This memory is powered from the battery or auxiliary power supply during hibernation. The processor
software can save state information in this memory prior to hibernation, and can then recover the
state upon waking. The non-volatile memory can be accessed through the HIBDATA registers.
Power Control
Important:
The Hibernation module controls power to the processor through the use of the HIB pin, which is
intended to be connected to the enable signal of the external regulator(s) providing 3.3 V and/or
2.5 V to the microcontroller. When the HIB signal is asserted by the Hibernation module, the external
regulator is turned off and no longer powers the microcontroller. The Hibernation module remains
powered from the VBAT supply, which could be a battery or an auxiliary power source. Hibernation
mode is initiated by the microcontroller setting the HIBREQ bit of the HIBCTL register. Prior to doing
this, a wake-up condition must be configured, either from the external WAKE pin, or by using an RTC
match.
The Hibernation module is configured to wake from the external WAKE pin by setting the PINWEN
bit of the HIBCTL register. It is configured to wake from RTC match by setting the RTCWEN bit. Either
one or both of these bits can be set prior to going into hibernation. The WAKE pin includes a weak
internal pull-up. Note that both the HIB and WAKE pins use the Hibernation module's internal power
supply as the logic 1 reference.
When the Hibernation module wakes, the microcontroller will see a normal power-on reset. It can
detect that the power-on was due to a wake from hibernation by examining the raw interrupt status
The Hibernation Module requires special system implementation considerations since
it is intended to power-down all other sections of its host device. The system
power-supply distribution and interfaces of the system must be driven to 0 V
powered down with the same regulator controlled by HIB. See “Hibernation
Module” on page 377 for more details.
Preliminary
July 25, 2008
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