ATmega328P datasheet(30/448 Pages) ATMEL

30 / 448 page

8161D–AVR–10/09

ATmega48PA/88PA/168PA/328P

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.

8.4

Full Swing Crystal Oscillator

Pins XTAL1 and XTAL2 are input and output, respectively, of an inverting amplifier which can be

configured for use as an On-chip Oscillator, as shown in Figure 8-2 on page 29. Either a quartz

crystal or a ceramic resonator may be used.

This Crystal Oscillator is a full swing oscillator, with rail-to-rail swing on the XTAL2 output. This is

useful for driving other clock inputs and in noisy environments. The current consumption is

higher than the ”Low Power Crystal Oscillator” on page 28. Note that the Full Swing Crystal

Oscillator will only operate for V

CC = 2.7 - 5.5 volts.

C1 and C2 should always be equal for both crystals and resonators. The optimal value of the

capacitors depends on the crystal or resonator in use, the amount of stray capacitance, and the

electromagnetic noise of the environment. Some initial guidelines for choosing capacitors for

use with crystals are given in Table 8-6 on page 31. For ceramic resonators, the capacitor val-

ues given by the manufacturer should be used.

The operating mode is selected by the fuses CKSEL3..1 as shown in Table 8-5.

Notes:

1. If 8 MHz frequency exceeds the specification of the device (depends on V

CC), the CKDIV8

Fuse can be programmed in order to divide the internal frequency by 8. It must be ensured

that the resulting divided clock meets the frequency specification of the device.

Crystal Oscillator, BOD

enabled

16K CK

14CK

Crystal Oscillator, fast

rising power

16K CK

14CK + 4.1 ms

Crystal Oscillator, slowly

rising power

16K CK

14CK + 65 ms

Table 8-4.

Start-up Times for the Low Power Crystal Oscillator Clock Selection (Continued)

Oscillator Source /

Power Conditions

Start-up Time from

Power-down and

Power-save

Additional Delay

from Reset

CC = 5.0V)

CKSEL0

SUT1..0

Table 8-5.

Full Swing Crystal Oscillator operating modes

Frequency Range(1)

(MHz)

Recommended Range for

Capacitors C1 and C2 (pF)

CKSEL3..1

0.4 - 20

12 - 22

011

ATmega328P Fiches technique(PDF) 30 Page - ATMEL Corporation

ATmega328P Fiches technique(HTML) 30 Page - ATMEL Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Fiches technique Télécharger

Lien URL