ATMEGA8515-16PI(2010) View Datasheet(PDF) - Atmel Corporation

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ATMEGA8515-16PI
(Rev.:2010)

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

Atmel Corporation 

External RC Oscillator

For timing insensitive applications, the external RC configuration shown in Figure 20

can be used. The frequency is roughly estimated by the equation f = 1/(3RC). C should

be at least 22 pF. By programming the CKOPT Fuse, the user can enable an internal

36 pF capacitor between XTAL1 and GND, thereby removing the need for an external

capacitor.

Figure 20. External RC Configuration

VCC

R

NC

C

XTAL2

XTAL1

GND

The Oscillator can operate in four different modes, each optimized for a specific fre-

quency range. The operating mode is selected by the fuses CKSEL3..0 as shown in

Table 10.

Table 10. External RC Oscillator Operating Modes

CKSEL3..0

0101

Frequency Range (MHz)

0.1 - 0.9

0110

0.9 - 3.0

0111

3.0 - 8.0

1000

8.0 - 12.0

When this Oscillator is selected, start-up times are determined by the SUT Fuses as

shown in Table 11.

Table 11. Start-up Times for the External RC Oscillator Clock Selection

SUT1..0

00

01

10

11

Start-up Time

from Power-down

18 CK

18 CK

18 CK

6 CK(1)

Additional Delay from

Reset (VCC = 5.0V)

–

4.1 ms

65 ms

4.1 ms

Recommended Usage

BOD enabled

Fast rising power

Slowly rising power

Fast rising power or BOD

enabled

Note: 1. This option should not be used when operating close to the maximum frequency of

the device.

38 ATmega8515(L)

2512K–AVR–01/10

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