AT89C2051X2 View Datasheet(PDF) - Atmel Corporation

Part Name

Description

Manufacturer

AT89C2051X2

8-bit Microcontroller with 2K Bytes Flash

Atmel Corporation 

Oscillator

Characteristics

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 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 2.

There are no requirements 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 1. Oscillator Connections

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

= 40 pF ± 10 pF for Ceramic Resonators

Figure 2. External Clock Drive Configuration

X2 Mode Description

The clock for the entire circuit and peripherals is normally divided by 2 before being

used by the CPU core and peripherals. This allows any cyclic ratio (duty cycle) to be

accepted on XTAL1 input. In X2 mode, as this divider is bypassed, the signals on

XTAL1 must have a cyclic ratio (duty cycle) between 40% to 60%. Figure 3 shows the

clock generation block diagram.

Figure 3. Clock Generation Block Diagram

X2 Mode

XTAL1

FXTAL

÷ 2 (XTAL1)/2

FOSC

State Machine: 6 Clock Cycles

CPU Control

4 AT89C2051x2

3285B–MICRO–10/03

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