Datasheet

SAM9263 [DATASHEET]
Atmel-6249N-ATARM-SAM9263-Datasheet_14-Mar-16
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26.3.1 Main Oscillator Connections
The Clock Generator integrates a Main Oscillator that is designed for a 3 to 20 MHz fundamental crystal. The
typical crystal connection is illustrated in Figure 26-3. The 1 k
Ω resistor is only required for crystals with
frequencies lower than 8 MHz. For further details on the electrical characteristics of the Main Oscillator, see
Section 46.2 “DC Characteristics”.
Figure 26-3. Typical Crystal Connection
26.3.2 Main Oscillator Startup Time
The startup time of the Main Oscillator is given in Section 46.2 “DC Characteristics”. The startup time depends on
the crystal frequency and decreases when the frequency rises.
26.3.3 Main Oscillator Control
To minimize the power required to start up the system, the main oscillator is disabled after reset and slow clock is
selected.
The software enables or disables the main oscillator so as to reduce power consumption by clearing the MOSCEN
bit in the Main Oscillator Register (CKGR_MOR).
When disabling the main oscillator by clearing the MOSCEN bit in CKGR_MOR, the MOSCS bit in PMC_SR is
automatically cleared, indicating the main clock is off.
When enabling the main oscillator, the user must initiate the main oscillator counter with a value corresponding to
the startup time of the oscillator. This startup time depends on the crystal frequency connected to the main
oscillator.
When the MOSCEN bit and the OSCOUNT are written in CKGR_MOR to enable the main oscillator, the MOSCS
bit in PMC_SR (Status Register) is cleared and the counter starts counting down on the slow clock divided by 8
from the OSCOUNT value. Since the OSCOUNT value is coded with 8 bits, the maximum startup time is about 62
ms.
When the counter reaches 0, the MOSCS bit is set, indicating that the main clock is valid. Setting the MOSCS bit in
PMC_IMR can trigger an interrupt to the processor.
26.3.4 Main Clock Frequency Counter
The Main Oscillator features a Main Clock frequency counter that provides the quartz frequency connected to the
Main Oscillator. Generally, this value is known by the system designer; however, it is useful for the boot program to
configure the device with the correct clock speed, independently of the application.
The Main Clock frequency counter starts incrementing at the Main Clock speed after the next rising edge of the
Slow Clock as soon as the Main Oscillator is stable, i.e., as soon as the MOSCS bit is set. Then, at the 16th falling
edge of Slow Clock, the MAINRDY bit in CKGR_MCFR (Main Clock Frequency Register) is set and the counter
1K
XIN XOUT GND
AT91 Microcontroller