Atmel ATmega328P Xplained Mini MEGA328P-XMINI MEGA328P-XMINI Data Sheet
Product codes
MEGA328P-XMINI
35
ATmega48A/PA/88A/PA/168A/PA/328/P [DATASHEET]
Atmel-8271H-AVR- ATmega-Datasheet_08/2014
9.7
128kHz Internal Oscillator
The 128kHz internal Oscillator is a low power Oscillator providing a clock of 128kHz. The frequency is nominal
at 3V and 25
at 3V and 25
C. This clock may be select as the system clock by programming the CKSEL Fuses to “11” as
shown in
Note:
1.
Note that the 128kHz 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
Note:
1.
If the RSTDISBL fuse is programmed, this start-up time will be increased to
14CK + 4.1ms to ensure programming mode can be entered.
14CK + 4.1ms to ensure programming mode can be entered.
9.8
External Clock
To drive the device from an external clock source, XTAL1 should be driven as shown in
. To run the
device on an external clock, the CKSEL Fuses must be programmed to “0000” (see
).
Figure 9-4.
External Clock Drive Configuration
When this clock source is selected, start-up times are determined by the SUT Fuses as shown in
Table 9-13.
128kHz Internal Oscillator Operating Modes
Nominal Frequency
CKSEL3...0
128kHz
0011
Table 9-14.
Start-up Times for the 128kHz 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 + 4ms
01
Slowly rising power
6 CK
14CK + 64ms
10
Reserved
11
Table 9-15.
Crystal Oscillator Clock Frequency
Frequency
CKSEL3...0
0 - 20MHz
0000
PB7
EXTERNAL
CLOCK
SIGNAL
XTAL2
XTAL1
GND