LM3S3748 Datasheet, PDF (139/753 Pages) List of Unclassifed Manufacturers – Microcontroller

LM3S3748 Microcontroller
7.2.2
restriction on timing for back-to-back reads from the Hibernation module. Software may make use
of the WRC bit in the HIBCTL register to ensure that the required timing gap has elapsed. This bit is
cleared on a write operation and set once the write completes, indicating to software that another
write or read may be started safely. Software should poll HIBCTL for WRC=1 prior to accessing any
affected register. The following registers are subject to this timing restriction:
■ Hibernation RTC Counter (HIBRTCC)
■ Hibernation RTC Match 0 (HIBRTCM0)
■ Hibernation RTC Match 1 (HIBRTCM1)
■ Hibernation RTC Load (HIBRTCLD)
■ Hibernation RTC Trim (HIBRTCT)
■ Hibernation Data (HIBDATA)
Clock Source
The Hibernation module must be clocked by an external source, even if the RTC feature will not be
used. An external oscillator or crystal can be used for this purpose. To use a crystal, a 4.194304-MHz
crystal is connected to the XOSC0 and XOSC1 pins. This clock signal is divided by 128 internally to
produce the 32.768-kHz clock reference. To use a more precise clock source, a 32.768-kHz oscillator
can be connected to the XOSC0 pin. See Figure 7-2 on page 140 and Figure 7-3 on page 141. Note
that these diagrams only show the connection to the Hibernation pins and not to the full system.
See “Hibernation Module” on page 697 for specific values.
The clock source is enabled by setting the CLK32EN bit of the HIBCTL register. The type of clock
source is selected by setting the CLKSEL bit to 0 for a 4.194304-MHz clock source, and to 1 for a
32.768-kHz clock source. If the bit is set to 0, the input clock is divided by 128, resulting in a
32.768-kHz clock source. If a crystal is used for the clock source, the software must leave a delay
of t_{XOSC_SETTLE} after setting 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 oscillator is used for
the clock source, no delay is needed.
April 08, 2008
139
Preliminary