LM3S5G51 Datasheet, PDF (192/1266 Pages) Texas Instruments – Stellaris® LM3S5G51 Microcontroller

System Control
Figure 5-4. Power Architecture
VDDC
Internal
GND
Logic and PLL
VDDC
GND
LDO
Low-Noise
LDO
+3.3V
VDD
VDD
I/O Buffers
GND
GND
VDDA
VDDA
Analog Circuits
GNDA
GNDA
5.2.5
5.2.5.1
Clock Control
System control determines the control of clocks in this part.
Fundamental Clock Sources
There are multiple clock sources for use in the microcontroller:
■ Precision Internal Oscillator (PIOSC). The precision internal oscillator is an on-chip clock
source that is the clock source the microcontroller uses during and following POR. It does not
require the use of any external components and provides a clock that is 16 MHz ±1% at room
temperature and ±3% across temperature. The PIOSC allows for a reduced system cost in
applications that require an accurate clock source. If the main oscillator is required, software
must enable the main oscillator following reset and allow the main oscillator to stabilize before
changing the clock reference. If the Hibernation Module clock source is a 32.768-kHz oscillator,
the precision internal oscillator can be trimmed by software based on a reference clock for
increased accuracy.
■ Main Oscillator (MOSC). The main oscillator provides a frequency-accurate clock source by
one of two means: an external single-ended clock source is connected to the OSC0 input pin, or
an external crystal is connected across the OSC0 input and OSC1 output pins. If the PLL is being
used, the crystal value must be one of the supported frequencies between 3.579545 MHz to
192
January 23, 2012
Texas Instruments-Production Data