ATTINY261A-MU Atmel, ATTINY261A-MU Datasheet - Page 29

• Manufacturer Part Number: ATTINY261A-MU
• Description: NO NEW DESIGNS, USE TINY261A-XU - 20MHZ, QFN/MLF,IND TEMP, G
• Manufacturer: Atmel

6.2.4
6.2.5
8197B–AVR–01/10
Internal 128 kHz Oscillator
Low-Frequency Crystal Oscillator
It is possible to reach a higher accuracy than factory calibration by changing the OSCCAL regis-
ter from software. See
this calibration is shown as User calibration in
When this oscillator is used as device clock, the Watchdog Oscillator will still be used for the
Watchdog Timer and for the Reset Time-out. For more information on the pre-programmed cali-
bration value, see section
The 128 kHz internal oscillator is a low power oscillator providing a clock of 128 kHz. The fre-
quency depends on supply voltage, temperature and batch variations. This clock may be select
as the system clock by programming the CKSEL Fuses to “0011”.
When this clock source is selected, start-up times are determined by the SUT Fuses as shown in
Table
Table 6-8.
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 ‘0100’. The crystal should be connected
as shown in
When this oscillator is selected, start-up times are determined by the SUT fuses as shown in
Table
Table 6-9.
Notes:
Table 6-10.
ATtiny261A/461A/861A
SUT1:0
SUT1:0
00
01
10
11
00
01
10
11
6-8.
6-9.
1. If the RSTDISBL fuse is programmed, this start-up time will be increased to 14CK + 4 ms to
1. These options should be used only if frequency stability at start-up is not important.
Device
ensure programming mode can be entered.
Figure
Start-up Time from Power-
Start-up Times for the 128 kHz Internal Oscillator
Start-up Times for the Low Frequency Crystal Oscillator Clock Selection
Capacitance for Low-Frequency Crystal Oscillator
from Power Down
32K (32768) CK
down and Power-save
1K (1024) CK
1K (1024) CK
Start-up Time
6-4. To find suitable capacitors please consult the manufacturer’s datasheet.
“OSCCAL – Oscillator Calibration Register” on page
6 CK
6 CK
6 CK
“Calibration Byte” on page
(1)
(1)
32 kHz Osc. Type
System Osc.
Additional Delay
from Reset
Additional Delay from
64 ms
64 ms
Table 19-2 on page
4 ms
Reserved
Reserved
14CK + 64 ms
14CK + 4 ms
14CK
169.
Reset
Cap (Xtal1/Tosc1)
(1)
16 pF
Recommended usage
Fast rising power or BOD enabled
Slowly rising power
Stable frequency at start-up
186.
BOD enabled
Fast rising power
Slowly rising power
Recommended Usage
32. The accuracy of
Cap (Xtal2/Tosc2)
6 pF
29