Datasheet

30
ATtiny25/45/85 [DATASHEET]
2586Q–AVR–08/2013
ment. Some initial guidelines for choosing capacitors for use with crystals are given in Table 6-12 below. For
ceramic resonators, the capacitor values given by the manufacturer should be used.
Notes: 1. This option should not be used with crystals, only with ceramic resonators.
The Oscillator can operate in three different modes, each optimized for a specific frequency range. The operating
mode is selected by the fuses CKSEL[3:1] as shown in Table 6-12.
The CKSEL0 Fuse together with the SUT[1:0] Fuses select the start-up times as shown in Table 6-13.
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 sta-
bility at start-up is not important for the application.
6.2.7 Default Clock Source
The device is shipped with CKSEL = “0010”, SUT = “10”, and CKDIV8 programmed. The default clock source set-
ting is therefore the Internal RC Oscillator running at 8 MHz with longest start-up time and an initial system clock
prescaling of 8, resulting in 1.0 MHz system clock. This default setting ensures that all users can make their
desired clock source setting using an In-System or High-voltage Programmer.
Table 6-12. Crystal Oscillator Operating Modes
CKSEL[3:1] Frequency Range (MHz)
Recommended Range for Capacitors C1 and
C2 for Use with Crystals (pF)
100
(1)
0.4 - 0.9 –
101 0.9 - 3.0 12 - 22
110 3.0 - 8.0 12 - 22
111 8.0 - 12 - 22
Table 6-13. Start-up Times for the Crystal Oscillator Clock Selection
CKSEL0 SUT[1:0]
Start-up Time from
Power-down
Additional Delay
from Reset Recommended Usage
0 00 258 CK
(1)
14CK + 4 ms
Ceramic resonator,
fast rising power
0 01 258 CK
(1)
14CK + 64 ms
Ceramic resonator,
slowly rising power
0 10 1K (1024) CK
(2)
14CK
Ceramic resonator,
BOD enabled
0 11 1K (1024)CK
(2)
14CK + 4 ms
Ceramic resonator,
fast rising power
1 00 1K (1024)CK
(2)
14CK + 64 ms
Ceramic resonator,
slowly rising power
1 01 16K (16384) CK 14CK
Crystal Oscillator,
BOD enabled
1 10 16K (16384) CK 14CK + 4 ms
Crystal Oscillator,
fast rising power
1 11 16K (16384) CK 14CK + 64 ms
Crystal Oscillator,
slowly rising power