AT89LP213 datasheet(12/96 Pages) ATMEL

12 / 96 page

3538C–MICRO–06/08

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 in some cases, external capacitors C1 and C2 may NOT be required due to the on-

chip capacitance of the XTAL1 and XTAL2 inputs (approximately 10 pF each). 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:

C1, C2 = 5 pF

± 5pF for Crystals

=5 pF

± 5pF for Ceramic Resonators

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

XTAL2 (P3.3)

GND

XTAL1 (P3.2)

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