![](http://datasheet.mmic.net.cn/30000/MQ83C154DXXX-25-883R_datasheet_2377229/MQ83C154DXXX-25-883R_75.png)
75
6384E–ATARM–05-Feb-10
AT91SAM9G20
13.3
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 Management 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, T
Table13-1 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 13-2 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 13-3 defines the crystals supported by the
Boot Program.
Note:
Booting either on USB or on DBGU is possible with any of these input frequencies.
Table 13-1.
Crystals Supported by Software Auto-Detection (MHz)
3.0
8.0
18.432
Other
Boot in DBGU
Yes
Boot on USB
Yes
No
Table 13-2.
Crystals Supported by Software Auto-Detection (MHz)
3.0
8.0
20
50
Other
Boot in DBGU
Yes
Boot on USB
Yes
No
Table 13-3.
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