LM3S9GN5 Datasheet, PDF (197/1388 Pages) Texas Instruments – ARM and Thumb are registered trademarks and Cortex is a trademark

Figure 5-4. Power Architecture
VDDC
VDDC
LDO
+3.3V
VDD
VDD
Internal
Logic and PLL
Low-Noise
LDO
I/O Buffers
Stellaris^® LM3S9GN5 Microcontroller
GND
GND
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.
■ 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
16.384 MHz (inclusive). If the PLL is not being used, the crystal may be any one of the supported
frequencies between 1 MHz to 16.384 MHz. The single-ended clock source range is from DC
January 23, 2012
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