Table 7-2. HIB Clock Source Configurations (continued)
OSCBYPOSCSELCLK32ENHIB Clock Source
011Low-frequency internal oscillator (HIB LFIOSC)
a
a. The frequency can have wide variations; refer to “Hibernation Clock Source Specifications” on page 1837 for more details.
To use an external 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 537 and Figure 7-3 on page 537.
Alternatively, a low frequency oscillator source (HIB LFIOSC) present in the Hibernation module
can be a clock source. (The frequency can have wide variations; refer to “Hibernation Clock Source
Specifications” on page 1837 for more details.) The intent of this source is to provide an internal low
power clock source to enable the use of the asynchronous pin wakes and memory storage without
the requirement of an external crystal. To enable the HIB LFIOSC to be the clock source for the
Hibernation module, both the OSCSEL bit and the CLK32EN bit in the Hibernation Control (HIBCTL)
register must be set.
Note: The HIB low-frequency oscillator (HIB LFIOSC) has a wide frequency variation, therefore
the RTC is not accurate when using this clock source. It is not recommended to use the
HIB LFIOSC as an RTC clock source.
The Hibernation module is enabled by setting the CLK32EN bit of the HIBCTL register. The CLK32EN
bit must be set before accessing any other Hibernation module register. The type of clock source
used for the HIB module is selected by setting the OSCSEL and OSCBYP bit of the HIBCTL register.
If the internal low frequency precision oscillator is used as the clock source, the OSCSEL bit should
be set to a 1 at the same time the CLK32EN bit is set. 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 537. 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 1845 for more information.
June 18, 2014536
Texas Instruments-Production Data
Hibernation Module
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