attiny11 ATMEL Corporation, attiny11 Datasheet - Page 10

• Manufacturer Part Number: attiny11
• Description: 8-bit Microcontroller With 1k Byte Flash
• Manufacturer: ATMEL Corporation

System Clock and
Clock Options
Internal RC Oscillator
ATtiny12 Calibrated
Internal RC Oscillator
Crystal Oscillator
10
ATtiny11/12
The device has the following clock source options, selectable by Flash fuse bits as
shown:
Table 3. Device Clocking Options Select
Note:
The various choices for each clocking option give different start-up times as shown in
Table 8 on page 23 and Table 10 on page 25.
The internal RC oscillator option is an on-chip oscillator running at a fixed frequency of 1
MHz in ATtiny11 and 1.2 MHz in ATtiny12. If selected, the device can operate with no
external components. The device is shipped with this option selected. On ATtiny11, the
Watchdog Oscillator is used as a clock, while ATtiny12 uses a separate calibrated
oscillator.
In ATtiny12, the calibrated internal oscillator provides a fixed 1.2 MHz (nominal) clock at
5V and 25°C. This clock may be used as the system clock. See the section “System
Clock and Clock Options” on page 10 for information on how to select this clock as the
system clock. This oscillator can be calibrated by writing the calibration byte to the OSC-
CAL register. When this oscillator is used as the chip clock, the Watchdog Oscillator will
still be used for the Watchdog Timer and for the reset time-out. For details on how to use
the pre-programmed calibration value, see the section “Calibration Byte in ATtiny12” on
page 49. At 5V and 25
± 1% of the nominal frequency.
XTAL1 and XTAL2 are input and output, respectively, of an inverting amplifier which can
be configured for use as an on-chip oscillator, as shown in Figure 5. Either a quartz
crystal or a ceramic resonator may be used. Maximum frequency for crystal and resona-
tors is 4 MHz. Minimum voltage for running on a low-frequency crystal is 2.5V.
Figure 5. Oscillator Connections (
device, an HC buffer should be connected as indicated in the figure.
Device Clocking Option
External Crystal/Ceramic Resonator
External Low-frequency Crystal
External RC Oscillator
Internal RC Oscillator
External Clock
Reserved
“1” means unprogrammed, “0” means programmed.
o
C, the pre-programmed calibration byte gives a frequency within
When using the MCU Oscillator as a clock for an external
HC
MAX 1 HC BUFFER
C2
C1
ATtiny11 CKSEL2..0
Other Options
111
110
101
100
000
XTAL2
XTAL1
GND
)
ATtiny12 CKSEL3..0
1111 - 1010
1001 - 1000
0111 - 0101
0100 - 0010
0001 - 0000
1006F–AVR–06/07
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