Rainbow Electronics ATmega128RFA1 - Manual (Page 150)

150
8266A-MCU Wireless-12/09
ATmega128RFA1
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 calibration value, see the section
"Calibration Byte" on page 467 .
Table 11-3. Internal Calibrated RC Oscillator Operating Modes
(1)(2)
Frequency Range (MHz) CKSEL3:0
9.6 ... 22.4 0010
Notes: 1. The device is shipped with this option selected.
When this Oscillator is selected, start-up times are determined by the SUT Fuses as
shown in the following table.
Table 11-4. Start-up times for the internal calibrated RC Oscillator clock selection
Power Conditions Start-up Time from Power-
down and Power-save Additional Delay from
Reset SUT1:0
BOD enabled 6 CK 14CK 00
Fast rising power 6 CK 14CK + 4.0 ms 01
Slowly rising power 6 CK 14CK + 64 ms
(1)
10
Reserved 11
Notes: 1. The device is shipped with this option selected
11.5 128 kHz Internal Oscillator
The 128 kHz Internal Oscillator is an ultra-low power RC oscillator providing a clock of
approximate 128 kHz nominal frequency. This clock may be selected as the system
clock by programming the CKSEL Fuses to “0011” as shown in the following table.
Table 11-5. 128 kHz Internal Oscillator Operating Modes
(1)
Nominal Frequency CKSEL3:0
128 kHz 0011
Notes: 1. Note that the 128 kHz oscillator is a very low power clock source, and is not
designed for high accuracy
When this clock source is selected, start-up times are determined by the SUT Fuses as
shown in the following table.
Table 11-6. Start-up Times for the 128 kHz Internal Oscillator
Power Conditions Start-up Time from Power-down
and Power-save Additional Delay from
Reset SUT1:0
BOD enabled 6 CK 14CK 00
Fast rising power 6 CK 14CK + 4.1 ms 01
Slowly rising power 6 CK 14CK + 64 ms 10
Reserved 11
11.6 External Clock
To drive the device from an external clock source, CLKI should be used as shown in
Figure 11-2 on page 151. To run the device on an external clock, the CKSEL Fuses
must be programmed to “0000”.