attiny25v ATMEL Corporation, attiny25v Datasheet - Page 29

• Manufacturer Part Number: attiny25v
• Description: Microcontroller With 2/4/8k Bytes In-system Programmable Flash
• Manufacturer: ATMEL Corporation

6.2.4
6.2.5
6.2.6
2586K–AVR–01/08
Internal 128 kHz Oscillator
Low-Frequency Crystal Oscillator
Crystal Oscillator / Ceramic Resonator
The 128 kHz internal Oscillator is a low power Oscillator providing a clock of 128 kHz. The fre-
quency is nominal at 3V and 25°C. This clock may be select as the system clock by
programming the CKSEL Fuses to “0100”.
When this clock source is selected, start-up times are determined by the SUT Fuses as shown in
Table
Table 6-9.
Note:
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
the manufacturer’s datasheet.
When this oscillator is selected, start-up times are determined by the SUT fuses as shown in
Table
Table 6-10.
Notes:
XTAL1 and XTAL2 are input and output, respectively, of an inverting amplifier which can be con-
figured for use as an On-chip Oscillator, as shown in
ceramic resonator may be used.
SUT1:0
SUT1:0
00
01
10
11
00
01
10
11
6-9.
6-10.
1. If the RSTDISBL fuse is programmed, this start-up time will be increased to 14CK + 4 ms to
1. These options should only be used if frequency stability at start-up is not important for the
ensure programming mode can be entered.
application.
Figure
Start-up Times for the 128 kHz Internal Oscillator
Start-up Times for the Low Frequency Crystal Oscillator Clock Selection
Start-up Time from
32K (32768) CK
1K (1024) CK
1K (1024) CK
Start-up Time from
Power Down
6-5. To find suitable load capacitance for a 32.768 kHz crysal, please consult
Power-down
6 CK
6 CK
6 CK
(1)
(1)
Additional Delay from
Reset (V
Additional Delay from
64 ms
64 ms
Reserved
4 ms
Reserved
14CK + 64 ms
14CK + 4 ms
CC
14CK
= 5.0V)
Reset
Figure
(1)
6-5. Either a quartz crystal or a
Recommended usage
Fast rising power or BOD
enabled
Slowly rising power
Stable frequency at start-up
ATtiny25/45/85
BOD enabled
Fast rising power
Slowly rising power
Recommended Usage
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