ATA5771_09 ATMEL [ATMEL Corporation], ATA5771_09 Datasheet - Page 82

• Manufacturer Part Number: ATA5771_09
• Description: Microcontroller with UHF ASK/FSK Transmitter
• Manufacturer: ATMEL [ATMEL Corporation]

7.6
7.7
7701C–AVR–12/08
Calibrated Internal RC Oscillator
External Clock
By default, the Internal RC Oscillator provides an approximate 8 MHz clock. Though voltage and
temperature dependent, this clock can be very accurately calibrated by the the user. See
22-2 on page 181
shipped with the CKDIV8 Fuse programmed. See
more details.
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-
ibrates the RC Oscillator. The accuracy of this calibration is shown as Factory calibration in
Table 22-2 on page
By changing the OSCCAL register from SW, see
page
The accuracy of this calibration is shown as User calibration in
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 more information on the pre-programmed cali-
bration value, see the section
Table 7-6.
Note:
When this Oscillator is selected, start-up times are determined by the SUT Fuses as shown in
Table 7-7 on page
Table 7-7.
Note:
To drive the device from an external clock source, CLKI should be driven as shown in
on page
“0000”.
SUT1..0
10
00
01
11
32, it is possible to get a higher calibration accuracy than by using the factory calibration.
(1)
7-6. If selected, it will operate with no external components. During reset, hardware loads
1. The device is shipped with this option selected.
1. The device is shipped with this option selected.
30. To run the device on an external clock, the CKSEL Fuses must be programmed to
CKSEL3..0
Internal Calibrated RC Oscillator Operating Modes
Start-up Times for the Internal Calibrated RC Oscillator Clock Selection
0010
from Power-down
and
29..
(1)
181.
Start-up Time
”Internal Oscillator Speed” on page 205
6 CK
6 CK
6 CK
”Calibration Byte” on page
Additional Delay from
Reset (V
Reserved
”Oscillator Calibration Register – OSCCAL” on
14CK + 64 ms
14CK + 4 ms
”System Clock Prescaler” on page 31
14CK
CC
166.
Nominal Frequency
= 5.0V)
8.0 MHz
Table 22-2 on page
for more details. The device is
ATtiny24/44/84
Recommended Usage
BOD enabled
Fast rising power
Slowly rising power
181.
Figure 7-3
Table
for
29