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AT89S51

8-bit Microcontroller with 4K Bytes In-System Programmable Flash

Atmel Corporation 

Figure 10-1. Interrupt Sources

0

INT0

IE0

1

TF0

0

INT1

IE1

1

TF1

TI

RI

11. Oscillator Characteristics

XTAL1 and XTAL2 are the input and output, respectively, of an inverting amplifier that can be

configured for use as an on-chip oscillator, as shown in Figure 11-1. 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 11-2. There are no

requirements on the duty cycle of the external clock signal, since the input to the internal clock-

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

time specifications must be observed.

Figure 11-1. Oscillator Connections

C2

XTAL2

C1

XTAL1

GND

Note: C1, C2 = 30 pF ± 10 pF for Crystals

= 40 pF ± 10 pF for Ceramic Resonators

12 AT89S51

2487D–MICRO–6/08

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