Datasheet

ATmega48A/PA/88A/PA/168A/PA/328/P
 2018 Microchip Technology Inc. Data Sheet Complete DS40002061A-page 39
Notes: 1. This is the recommended CKSEL settings for the difference frequency ranges.
2. This option should not be used with crystals, only with ceramic resonators.
3. If the crystal 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.
The CKSEL0 Fuse together with the SUT1...0 Fuses select the start-up times as shown in Table 9-4.
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 frequency of the device, and if
frequency stability at start-up is not important for the application.
9.4 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 9-2 on page 38. Either a quartz crystal or a ceramic resonator
may be used.
Table 9-3. Low Power Crystal Oscillator Operating Modes
(3)
Frequency Range
(MHz)
Recommended Range for
Capacitors C1 and C2 (pF) CKSEL3...1
(1)
0.4 - 0.9 – 100
(2)
0.9 - 3.0 12 - 22 101
3.0 - 8.0 12 - 22 110
8.0 - 16.0 12 - 22 111
Table 9-4. Start-up Times for the Low Power Crystal Oscillator Clock Selection
Oscillator Source /
Power Conditions
Start-up Time from
Power-down and
Power-save
Additional Delay
from Reset
(V
CC
= 5.0V) CKSEL0 SUT1...0
Ceramic resonator, fast
rising power
258 CK 14CK + 4.1ms
(1)
0 00
Ceramic resonator, slowly
rising power
258 CK 14CK + 65ms
(1)
0 01
Ceramic resonator, BOD
enabled
1K CK 14CK
(2)
0 10
Ceramic resonator, fast
rising power
1K CK 14CK + 4.1ms
(2)
0 11
Ceramic resonator, slowly
rising power
1K CK 14CK + 65ms
(2)
1 00
Crystal Oscillator, BOD
enabled
16K CK 14CK 1 01
Crystal Oscillator, fast
rising power
16K CK 14CK + 4.1ms 1 10
Crystal Oscillator, slowly
rising power
16K CK 14CK + 65ms 1 11