TM4C123BE6PM Datasheet, PDF (484/1276 Pages) Texas Instruments – Tiva TM4C123BE6PM Microcontroller

Hibernation Module
7.3.2
Back-to-back reads from Hibernation module registers have no timing restrictions. Reads are
performed at the full peripheral clock rate.
Hibernation Clock Source
In systems where the Hibernation module is used, the module must be clocked by an external source
that is independent from the main system clock, even if the RTC feature is not used. An external
oscillator or crystal is used for this purpose. To use a crystal, a 32.768-kHz crystal is connected to
the XOSC0 and XOSC1 pins. Alternatively, a 32.768-kHz oscillator can be connected to the XOSC0
pin, leaving XOSC1 unconnected. Care must be taken that the voltage amplitude of the 32.768-kHz
oscillator is less than V_BAT, otherwise, the Hibernation module may draw power from the oscillator
and not V_BAT during hibernation. See Figure 7-2 on page 484 and Figure 7-3 on page 485.
The Hibernation clock source is enabled by setting the CLK32EN bit of the HIBCTL register. The
CLK32EN bit must be set before accessing any other Hibernation module register. If a crystal is
used for the clock source, the software must leave a delay of t_{HIBOSC_START} after writing to the
CLK32EN bit and before any other accesses to the Hibernation module registers. The delay allows
the crystal to power up and stabilize. If an external oscillator is used for the clock source, no delay
is needed. When using an external clock source, the OSCBYP bit in the HIBCTL register should be
set. When using a crystal clock source, the GNDX pin should be connected to digital ground along
with the crystal load capacitors, as shown in Figure 7-2 on page 484. When using an external clock
source, the GNDX pin should be connected to digital ground.
Note: In the figures below the parameters R_BAT and C_BAT have recommended values of 51Ω ±5%
and 0.1µF ±5%, respectively. See “Hibernation Module” on page 1251 for more information.
Figure 7-2. Using a Crystal as the Hibernation Clock Source with a Single Battery Source
Input
Voltage
Regulator
or Switch
IN OUT
EN
C₁
X₁
C₂
Tiva™ Microcontroller
VDD
XOSC0
XOSC1
GNDX
Open drain
external wake
up circuit
HIB
WAKE
VBAT
R_PU
GND
R_BAT
C_BAT
3V
Battery
Note:
Some devices may not supply the GNDX signal. If GNDX is absent, the crystal load capacitors can
be tied to GND externally. See “Signal Tables” on page 1200 for pins specific to your device.
X₁ = Crystal frequency is f_{XOSC_XTAL}.
C_1,2 = Capacitor value derived from crystal vendor load capacitance specifications.
R_PU = Pull-up resistor is 200 kΩ
R_BAT = 51Ω ±5%
C_BAT = 0.1µF ±20%
See “Hibernation Clock Source Specifications” on page 1243 for specific parameter values.
484
June 12, 2014
Texas Instruments-Production Data