at91sam9g45 ATMEL Corporation, at91sam9g45 Datasheet - Page 32

• Manufacturer Part Number: at91sam9g45
• Description: At91 Arm Thumb-based Microcontrollers
• Manufacturer: ATMEL Corporation

8.6.1
8.6.2
8.6.3
32
AT91SAM9G45
Switch from Internal RC Oscillator to the 32768 Hz Crystal
Bypass the 32768 Hz Oscillator
Switch from 32768 Hz Crystal to the Internal RC Oscillator
Figure 8-3.
After a VDDBU power on reset, the default configuration is RCEN = 1, OSC32EN = 0 and OSC-
SEL = 0 allowing the system to start on the internal RC oscillator.
The programmer controls by software the slow clock switching and so must take precautions
during the switching phase.
To switch from internal RC oscillator to the 32768 Hz crystal, the programmer must execute the
following sequence:
The following step must be added to bypass the 32768 Hz Oscillator.
The same procedure must be followed to switch from 32768 Hz crystal to the internal RC
oscillator.
• Switch the master clock to a source different from slow clock (PLLA or PLLB or Main
• Enable the 32768 Hz oscillator by setting the bit OSCEN to 1.
• Wait 32768 Hz startup time for clock stabilization (software loop).
• Switch from internal RC to 32768 Hz by setting the bit OSCSEL to 1.
• Wait 5 slow clock cycles for internal resynchronization.
• Disable the RC oscillator by setting the bit RCEN to 0.
• An external clock must be connected on XIN32.
• Enable the bypass path OSC32BYP bit set to 1.
• Disable the 32768 Hz oscillator by setting the bit OSC32EN to 0.
• Switch the master clock to a source different from slow clock (PLLA or PLLB or Main
• Enable the internal RC oscillator by setting the bit RCEN to 1.
• Wait internal RC Startup Time for clock stabilization (software loop).
Oscillator) through the Power Management Controller.
Oscillator).
Slow Clock
XOUT32
XIN32
Clock Generator
Slow Clock
Oscillator
On Chip
RC OSC
RCEN
Slow Clock
SLCK
OSCSEL
OSC32EN
OSC32BYP
6438CS–ATARM–13-Oct-09