AT90CAN64 datasheet(40/431 Pages) ATMEL

40 / 431 page

7682C–AUTO–04/08

AT90CAN32/64/128

Notes:

1. These options should only be used when not operating close to the maximum frequency of the

device, and only if frequency stability at start-up is not important for the application. These

options are not suitable for crystals.

2. These options are intended for use with ceramic resonators and will ensure frequency stability

at start-up. They can also be used with crystals when not operating close to the maximum fre-

quency of the device, and if frequency stability at start-up is not important for the application.

5.5

Low-frequency Crystal Oscillator

To use a 32.768 kHz watch crystal as the clock source for the device, the low-frequency crystal

Oscillator must be selected by setting the CKSEL Fuses to “0100”, “0101”, “0110”, or “0111”.

The crystal should be connected as shown in Figure 5-3.

Figure 5-3.

Low-frequency Crystal Oscillator Connections

12-22 pF capacitors may be necessary if the parasitic impedance (pads, wires & PCB) is very

low.

Table 5-4.

Start-up Times for the Oscillator Clock Selection

CKSEL0

SUT1..0

Start-up Time from

Power-down and

Power-save

Additional Delay

from Reset

(VCC = 5.0V)

Recommended Usage

258 CK(1)

14 CK + 4.1 ms

Ceramic resonator, fast

rising power

258 CK(1)

14 CK + 65 ms

Ceramic resonator, slowly

rising power

1K CK(2)

14 CK

Ceramic resonator, BOD

enabled

1K CK(2)

14 CK + 4.1 ms

Ceramic resonator, fast

rising power

1K CK(2)

14 CK + 65 ms

Ceramic resonator, slowly

rising power

16K CK

14 CK

Crystal Oscillator, BOD

enabled

16K CK

14 CK + 4.1 ms

Crystal Oscillator, fast

rising power

16K CK

14 CK + 65 ms

Crystal Oscillator, slowly

rising power

XTAL2

XTAL1

GND

12 - 22 pF

32.768 KHz

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