4

0368H–MICRO–6/08

AT89C2051

4.7

XTAL2

Output from the inverting oscillator amplifier.

5.

Oscillator Characteristics

The XTAL1 and XTAL2 are the input and output, respectively, of an inverting amplifier which can

be configured for use as an on-chip oscillator, as shown in Figure 5-1. Either a quartz crystal or

ceramic resonator may be used. To drive the device from an external clock source, XTAL2

should be left unconnected while XTAL1 is driven as shown in Figure 5-2. There are no require-

ments on the duty cycle of the external clock signal, since the input to the internal clocking

circuitry is through a divide-by-two flip-flop, but minimum and maximum voltage high and low

time specifications must be observed.

Figure 5-1.

Oscillator Connections

Note:

C1, C2 = 30 pF

± 10 pF for Crystals

= 40 pF

± 10 pF for Ceramic Resonators

Figure 5-2.

External Clock Drive Configuration