attiny24v ATMEL Corporation, attiny24v Datasheet - Page 26

• Manufacturer Part Number: attiny24v
• Description: 8-bit Avr Microcontroller With 2/4/8k Bytes Insystem Programmable Flash
• Manufacturer: ATMEL Corporation

6.2.1
6.2.2
26
ATtiny24/44/84
External Clock
Calibrated Internal 8 MHz Oscillator
To drive the device from an external clock source, CLKI should be driven as shown in
on page
“0000”.
Figure 6-2.
When this clock source is selected, start-up times are determined by the SUT Fuses as shown in
Table
Table 6-3.
When applying an external clock, it is required to avoid sudden changes in the applied clock fre-
quency to ensure stable operation of the MCU. A variation in frequency of more than 2% from
one clock cycle to the next can lead to unpredictable behavior. It is required to ensure that the
MCU is kept in Reset during such changes in the clock frequency.
Note that the System Clock Prescaler can be used to implement run-time changes of the internal
clock frequency while still ensuring stable operation. See
for details.
By default, the Internal Oscillator provides an approximate 8 MHz clock. Though voltage and
temperature dependent, this clock can be very accurately calibrated by the user. See
on page 176
with the CKDIV8 Fuse programmed. See
This clock may be selected as the system clock by programming the CKSEL Fuses as shown in
Table
the pre-programmed calibration value into the OSCCAL Register and thereby automatically cal-
SUT1..0
00
01
10
11
6-3.
6-4. If selected, it will operate with no external components. During reset, hardware loads
26. To run the device on an external clock, the CKSEL Fuses must be programmed to
and
External Clock Drive Configuration
Start-up Times for the External Clock Selection
EXTERNAL
“Internal Oscillator Speed” on page 205
from Power-down
SIGNAL
Start-up Time
CLOCK
6 CK
6 CK
6 CK
“System Clock Prescaler” on page 30
Additional Delay
Reserved
14CK + 64 ms
14CK + 4 ms
from Reset
14CK
CLKI
GND
for more details. The device is shipped
“System Clock Prescaler” on page 30
BOD enabled
Fast rising power
Slowly rising power
Recommended
for more details.
Usage
8006H–AVR–10/09
Table 20-2
Figure 6-2