ATTINY25_07 Datasheet, PDF (25/201 Pages) ATMEL Corporation – 8-bit Microcontroller with 2/4/8K Bytes In-System Programmable Flash

ATtiny25/45/85 Auto
Table 6-4. Start-up Times for the Crystal Oscillator Clock Selection
CKSEL0 SUT1..0
0
00
Start-up Time from
Power-down and
Power-save
258 CK⁽¹⁾
Additional Delay
from Reset
(V_CC = 5.0V)
14CK + 4.1 ms
Recommended Usage
Ceramic resonator, fast
rising power
0
01
258 CK⁽¹⁾
14CK + 65 ms
Ceramic resonator, slowly
rising power
0
10
1K CK⁽²⁾
14CK
Ceramic resonator, BOD
enabled
0
11
1K CK⁽²⁾
14CK + 4.1 ms
Ceramic resonator, fast
rising power
1
00
1K CK⁽²⁾
14CK + 65 ms
Ceramic resonator, slowly
rising power
1
01
16K CK
14CK
Crystal Oscillator, BOD
enabled
1
10
16K CK
14CK + 4.1 ms
Crystal Oscillator, fast
rising power
1
11
16K CK
14CK + 65 ms
Crystal Oscillator, slowly
rising power
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.
Table 6-5.
SUT1..0
00
01
10
11
Start-up Times for the Low Frequency Crystal Oscillator Clock Selection
Start-up Time from
Power Down and Power
Save
1K CK⁽¹⁾
1K CK⁽¹⁾
Additional Delay from
Reset (V_CC = 5.0V)
4 ms
64 ms
Recommended usage
Fast rising power or BOD
enabled
Slowly rising power
32K CK
64 ms
Stable frequency at start-up
Reserved
Notes: 1. These options should only be used if frequency stability at start-up is not important for the
application.
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