5
6415B–ATARM–03-Oct-08
Application Note
5.
Clock Characteristics
5.1
On Chip RC Oscillator
5.2
Boot ROM Crystal Frequency Support
5.2.1
With Internal RC Oscillator
The following crystal descriptions only give acceptable USB clock frequency accuracy for the
Boot ROM on the AT91SAM9G20.
..
5.2.2
With External 32768 Hz Crystal
The following crystal descriptions only give acceptable USB clock frequency accuracy for Boot
ROM on the AT91SAM9G20.
.
Table 5-1.
RC characteristics
RC Characteristics
AT91SAM9260
AT91SAM9G20
Startup time
240 µs
150 µs
Table 5-2.
Reduced Crystal Table (MHz) OSCSEL = 0
3.0
8.0
18.432
Other
Boot on DBGU
Yes
Yes
Yes
Yes
Boot on USB
Yes
Yes
Yes
No
Table 5-3.
Reduced Crystal Table (MHz) OSCSEL = 0 and Main Oscillator is Bypassed
3.0
8.0
20.0
50.0
Other
Boot on DBGU
Yes
Yes
Yes
Yes
Yes
Boot on USB
Yes
Yes
Yes
Yes
No
Table 5-4.
Large Crystal Table (MHz) OSCSEL = 1
3.0
3.6864
3.84
4.0
4.9152
5.24288
6.0
6.144
6.4
6.5536
7.3728
8.0
9.8304
10.0
11.05920
12.0
12.288
14.31818
14.7456
16.0
16.367667
17.734470
18.432
20.0
Table 5-5.
Large Crystal Table (MHz) OSCSEL = 1 and Main Oscillator is Bypassed
3.0
3.6864
3.84
4.0
4.9152
5.24288
6.0
6.144
6.4
6.5536
7.3728
8.0
9.8304
10.0
11.05920
