ATMEGA48 datasheet(34/374 Pages) ATMEL

34 / 374 page

2545J–AVR–12/06

ATmega48/88/168

3. If 8 MHz frequency exceeds the specification of the device (depends on VCC), the CKDIV8

Fuse can be programmed in order to divide the internal frequency by 8.

When this Oscillator is selected, start-up times are determined by the SUT Fuses as shown in

Table 7-9 on page 34.

Note:

1. If the RSTDISBL fuse is programmed, this start-up time will be increased to

14CK + 4.1 ms to ensure programming mode can be entered.

The device is shipped with this option selected.

7.7

128 kHz Internal Oscillator

The 128 kHz internal Oscillator is a low power Oscillator providing a clock of 128 kHz. The fre-

quency is nominal at 3V and 25

°C. This clock may be select as the system clock by

programming the CKSEL Fuses to “11” as shown in Table 7-10.

Note:

1. The frequency is preliminary value. Actual value is TBD.

When this clock source is selected, start-up times are determined by the SUT Fuses as shown in

Table 7-11.

Note:

1. If the RSTDISBL fuse is programmed, this start-up time will be increased to

14CK + 4.1 ms to ensure programming mode can be entered.

Table 7-9.

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 (VCC = 5.0V)

SUT1..0

BOD enabled

6 CK

14CK(1)

Fast rising power

6 CK

14CK + 4.1 ms

Slowly rising power

6 CK

14CK + 65 ms(2)

Reserved

Table 7-10.

128 kHz Internal Oscillator Operating Modes

Nominal Frequency

CKSEL3..0

128 kHz

0011

Table 7-11.

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(1)

Fast rising power

6 CK

14CK + 4 ms

Slowly rising power

6 CK

14CK + 64 ms

Reserved

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