6 Clocks and crystal oscillators
There are three clock inputs available:
•
XIN0 / XOUT0
•
XIN1 / XOUT1
•
XIN32 / XOUT32
The recommendations below refer to XIN / XOUT, but apply to all the clock inputs.
6.1 External clock source
Figure 6-1.
External clock source schematic.
Table 6-1.
External clock source checklist.
Signal name
XIN
XOUT
Recommended pin connection
Connected to clock output from external clock source
Can be left unconnected or used as GPIO
Description
Up to VDDIO-volt square wave signal up to 50MHz
6.2 Crystal oscillator
Figure 6-2.
Crystal oscillator example schematic.
Table 6-2.
Crystal oscillator checklist.
Signal name
XIN
XOUT
Notes:
Recommended pin connection
Biasing capacitor, 22pF
(1)(2)
Biasing capacitor, 22pF
(1)(2)
1. These values are given only as a typical example. The capacitance, C, of the biasing capacitors can be computed
based on the crystal load capacitance, C
L
, and the internal capacitance, C
i
, of the MCU as follows:
C = 2(C
L
– C
i
)
The value of C
L
can be found in the crystal datasheet and the value of C
i
can be found in the MCU datasheet
2. Decoupling capacitor should be placed as close as possible to each pin in the signal group, and vias should be
avoided
Description
External crystal between 450kHz and 16MHz
8
AVR32768
32157A-AVR-12/10
ATMEL [ ATMEL CORPORATION ]
