Atmel ATtiny25 User Manual

25
7598H–AVR–07/09
ATtiny25/45/85
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.
6.5 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 CKSEL fuses to ‘0110’. The crystal should be connected
as shown in Figure 6-3. Refer to the 32 kHz Crystal Oscillator Application Note for details on
oscillator operation and how to choose appropriate values for C1 and C2.
When this oscillator is selected, start-up times are determined by the SUT fuses as shown in
Table 6-5.
Notes: 1. These options should only be used if frequency stability at start-up is not important for the
application.
Table 6-4. Start-up Times for the Crystal Oscillator Clock Selection
CKSEL0 SUT1..0
Start-up Time from
Power-down and
Power-save
Additional Delay
from Reset
(V
CC
= 5.0V) 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
010 1K CK
(2)
14CK
Ceramic resonator, BOD
enabled
011 1K CK
(2)
14CK + 4 ms
Ceramic resonator, fast
rising power
100 1K CK
(2)
14CK + 64 ms
Ceramic resonator, slowly
rising power
1 01 16K CK 14CK
Crystal Oscillator, BOD
enabled
1 10 16K CK 14CK + 4 ms
Crystal Oscillator, fast
rising power
1 11 16K CK 14CK + 64 ms
Crystal Oscillator, slowly
rising power
Table 6-5. Start-up Times for the Low Frequency Crystal Oscillator Clock Selection
SUT1..0
Start-up Time from
Power Down and Power
Save
Additional Delay from
Power On Reset
(V
CC
= 5.0V) Recommended usage
00 1K CK
(1)
4 ms
Fast rising power or BOD
enabled
01 1K CK
(1)
64 ms Slowly rising power
10 32K CK 64 ms Stable frequency at start-up
11 Reserved

Atmel ATtiny25 Specifications

General

Brand	Atmel
Model	ATtiny25
Category	Microcontrollers
Language	English