Datasheet

6
ATmega323(L)
1457E–11/01
Clock Options The device has the following clock source options, selectable by Flash fuse bits as
shown:
Note: “1” means unprogrammed, “0” means programmed.
The various choices for each clocking option give different start-up times as shown in
Table 6 on page 27.
Internal RC Oscillator The internal RC oscillator option is an On-chip oscillator running at a fixed frequency of
nominally 1 MHz. If selected, the device can operate with no external components. See
“Calibrated Internal RC Oscillator” on page 40 for information on calibrating this
oscillator.
Crystal Oscillator XTAL1 and XTAL2 are input and output, respectively, of an inverting amplifier which can
be configured for use as an On-chip oscillator, as shown in Figure 2. Either a quartz
crystal or a ceramic resonator may be used.
Figure 2. Oscillator Connections
Table 1. Device Clocking Options Select
Device Clocking Option CKSEL3..0
External Crystal/Ceramic Resonator 1111 - 1010
External Low-frequency Crystal 1001 - 1000
External RC Oscillator 0111 - 0101
Internal RC Oscillator 0100 - 0010
External Clock 0001 - 0000
XTAL2
XTAL1
GND
C2
C1