SAM3U Datasheet, PDF (38/59 Pages) ATMEL Corporation – AT91SAM ARM-based Flash MCU

The Slow Clock generator is based on a 32 kHz crystal oscillator and an embedded 32 kHz RC
oscillator. The Slow Clock defaults to the RC oscillator, but the software can enable the crystal
oscillator and select it as the Slow Clock source.
The Supply Controller starts up the device by enabling the Voltage Regulator, then it generates
the proper reset signals to the core power supply.
It also enables to set the system in different low power modes and to wake it up from a wide
range of events.
10.5 Clock Generator
The Clock Generator is made up of:
• One Low Power 32768 Hz Slow Clock Oscillator with bypass mode
• One Low Power RC Oscillator
• One 3 to 20 MHz Crystal Oscillator, which can be bypassed
• One Fast RC Oscillator factory programmed, 3 output frequencies can be selected: 4, 8 or 12
MHz. By default 4 MHz is selected. 8 MHz and 12 MHz output are factory calibrated.
• One 480 MHz UPLL providing a clock for the USB High Speed Device Controller. Input
frequency is 12 MHz (only).
• One 96 to 192 MHz programmable PLL (PLL A), capable to provide the clock MCK to the
processor and to the peripherals. The input frequency of the PLL A is between 8 and 16 MHz.
Figure 10-2. Clock Generator Block Diagram
Clock Generator
XIN32
XOUT32
On Chip
32k RC OSC
Slow Clock
Oscillator
XTALSEL
Slow Clock
SLCK
XIN
XOUT
12M Main
Oscillator
On Chip
12/8/4 MHz
RC OSC
Main Clock
MAINCK
MAINSEL
38 SAM3U Series
PLL B
Divider
/6 /8
PLL and
Divider A
Status Control
Power
Management
Controller
HSCK
UPLL Clock
UPLLCK
PLLA Clock
PLLACK
6430ES–ATARM–22-Aug-11