Datasheet

SAM9G20
DS60001516A-page 70  2017 Microchip Technology Inc.
12.3 Device Initialization
Initialization follows the steps described below:
1. Stack setup for Arm supervisor mode
2. Main Oscillator Frequency Detection
3. C variable initialization
4. PLL setup: PLLB is initialized to generate a 48 MHz clock necessary to use the USB Device. A register located in the Power Man-
agement Controller (PMC) determines the frequency of the main oscillator and thus the correct factor for the PLLB.
- If internal RC Oscillator is used (OSCSEL = 0) and Main Oscillator is active, TTable 12-1 defines the crystals supported by the
Boot Program when using the internal RC oscillator. also supported by the Boot Program.
Note: Any other crystal can be used but it prevents using the USB.
- If internal RC Oscillator is used (OSCSEL = 0) and Main Oscillator is bypassed, Table 12-2 defines the frequencies supported by
the Boot Program when bypassing the main oscillator.
Note: Any other crystal can be used but it prevents using the USB.
- If an external 32768 Hz Oscillator is used (OSCSEL = 1), defines the crystals supported by the Boot Program. Table 12-3 defines
the crystals supported by the Boot Program.
Note: Booting either on USB or on DBGU is possible with any of these input frequencies.
- If an external 32768 Hz Oscillator is used (OSCSEL = 1) and Main Oscillator is bypassed. Table 12-4 defines the crystals sup-
ported by the Boot Program.
Table 12-1: Crystals Supported by Software Auto-Detection (MHz)
3.0 8.0 18.432 Other
Boot in DBGU Yes Yes Yes Yes
Boot on USB Yes Yes Yes No
Table 12-2: Crystals Supported by Software Auto-Detection (MHz)
3.0 8.0 20 50 Other
Boot in DBGU Yes Yes Yes Yes Yes
Boot on USB Yes Yes Yes Yes No
Table 12-3: Crystals Supported by Software Auto-Detection (MHz)
3.0 3.2768 3.6864 3.84 4.0
4.433619 4.608 4.9152 5.0 5.24288
6.0 6.144 6.4 6.5536 7.159090
7.3728 7.864320 8.0 9.8304 10.0
11.05920 12.0 12.288 13.56 14.31818
14.7456 16.0 17.734470 18.432 20.0
Table 12-4: Input Frequencies Supported (OSCEL = 1)
3.0 3.2768 3.6864 3.84 4.0
4.433619 4.608 4.9152 5.0 5.24288
6.0 6.144 6.4 6.5536 7.159090
7.3728 7.864320 8.0 9.8304 10.0