LM3S2620 Luminary Micro, Inc, LM3S2620 Datasheet - Page 124

• Manufacturer Part Number: LM3S2620
• Description: Lm3s2620 Arm Microcontroller
• Manufacturer: Luminary Micro, Inc

Hibernation Module
7.2.2
124
Hibernation registers, or between a write followed by a read to those same registers. There is no
restriction on timing for back-to-back reads from the Hibernation module.
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 124 and Figure 7-3 on page 125. Note
that these diagrams only show the connection to the Hibernation pins and not to the full system.
See “Hibernation Module” on page 521 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
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.
Figure 7-2. Clock Source Using Crystal
Note:
XOSC_SETTLE
Voltage
R
R
See “Hibernation Module” on page 521 for specific parameter values.
TERM
PU
Input
= Pull-up resistor (1 M½).
= Optional series termination resistor.
after setting the CLK32EN bit and before any other accesses to the Hibernation
R
Regulator
or Switch
IN
PU
EN
OUT
C
1
external wake
Open drain
up circuit
Preliminary
X
1
C
2
R
L
Stellaris Microcontroller
VDD
XOSC0
XOSC1
HIB
WAKE
GND
VBAT
3 V
Battery
July 25, 2008