AT89LP213 datasheet(12/98 Pages) ATMEL

12 / 98 page

3538D–MICRO–10/09

AT89LP213/214

System Clock

The system clock is generated directly from one of three selectable clock sources. The three

sources are the on-chip crystal oscillator, external clock source, and internal RC oscillator. The

clock source is selected by the Clock Source User Fuses as shown in Table 9-1. No internal

clock division is used to generate the CPU clock from the system clock. See “User Configuration

Fuses” on page 72.

9.1

Crystal Oscillator

When enabled, the internal inverting oscillator amplifier is connected between XTAL1 and

XTAL2 for connection to an external quartz crystal or ceramic resonator as shown in Figure 9-1.

Note that the internal structure of the device adds about 10 pF of capacitance to both XTAL1

and XTAL2, so that in some cases an external capacitor may NOT be required. It is recom-

mended that a resistor R1 be connected to XTAL1, instead of load capacitor C1, for improved

startup performance. The total capacitance on XTAL1 or XTAL2, including the external load

capacitor plus internal device load, board trace and crystal loadings, should not exceed 20 pF.

When using the crystal oscillator, P3.2 and P3.3 will have their inputs and outputs disabled.

When using the crystal oscillator, XTAL2 should not be used to drive a board-level clock without

a buffer.

Figure 9-1.

Crystal Oscillator Connections

Note:

1. C2

0–10 pF for Crystals

0–10 pF for Ceramic Resonators

4–5 M

Table 9-1.

Clock Source Settings

Clock Source

Fuse 1

Clock Source

Fuse 0

Selected Clock Source

Crystal Oscillator

Reserved

External Clock on XTAL1

Internal 8 MHz RC Oscillator

~10 pF

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