Rainbow Electronics ATmega103L - Manual (Page 6)

ATmega603/103
6
Clock Options
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
Note: When using the MCU Oscillator as a clock for an external device, an HC buffer should be connected as indicated in the figure.
External Clock
To drive the device from an external clock source, XTAL2 should be left unconnected while XTAL1 is driven as shown in
Figure 3.
Figure 3. External Clock Drive Configuration
Timer Oscillator
For the Timer Oscillator pins, TOSC1 and TOSC2, the crystal is connected directly between the pins. No external capaci-
tors are needed. The oscillator is optimized for use with a 32,768 Hz watch crystal. An external clock signal applied to this
pin goes through the same amplifier having a bandwidth of 256 kHz. The external clock signal should therefore be in the
range 0 Hz - 256 kHz.
XTAL2
XTAL1
GND
C2
C1
MAX 1 HC BUFFER
HC
XTAL2
XTAL1
GND
NC
EXTERNAL
OSCILLATOR
SIGNAL