AT89LP428-20MU ATMEL [ATMEL Corporation], AT89LP428-20MU Datasheet - Page 21

• Manufacturer Part Number: AT89LP428-20MU
• Description: 8-bit Microcontroller with 4K/8K Bytes In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

6.1
6.2
3654A–MICRO–8/09
Crystal Oscillator
External Clock Source
When enabled, the internal inverting oscillator amplifier is connected between XTAL1 and
XTAL2 for connection to an external quartz crystal or ceramic resonator. The oscillator may
operate in either high-speed or low-speed mode. Low-speed mode is intended for 32.768 kHz
watch crystals and consumes less power than high-speed mode. The configuration as shown in
Figure 6-1
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 recommended 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, P4.0 and P4.1
will have their inputs and outputs disabled. Also, XTAL2 in crystal oscillator mode should not be
used to directly drive a board-level clock without a buffer.
Figure 6-1.
Note:
The external clock option disables the oscillator amplifier and allows XTAL1 to be driven directly
by an external clock source as shown in
general-purpose I/O P4.1, or configured to output a divided version of the system clock.
Figure 6-2.
1. C2
applies for both high and low speed oscillators. Note that the internal structure of the
R1
Crystal Oscillator Connections
External Clock Drive Configuration
= 0–10 pF for Crystals
= 0–10 pF for Ceramic Resonators
= 4–5 MΩ
NC, GPIO, or
CLKOUT
Oscillator
External
Signal
C2
R1
Figure
6-2. XTAL2 may be left unconnected, used as
XTAL2 (P4.1)
XTAL1 (P4.0)
GND
~10 pF
~10 pF
AT89LP428/828
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