ATtiny43U datasheet(26/182 Pages) ATMEL

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8048B–AVR–03/09

ATtiny43U

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

Table 6-5 below.

Note:

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

14CK + 4 ms to ensure programming mode can be entered.

The device is shipped with this option selected.

6.2.3

Internal 128 kHz 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 6-6 below.

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

Table 6-7 below.

Note:

1. If the RSTDISBL fuse is programmed, this start-up time will be increased to 14CK + 4 ms to

ensure programming mode can be entered.

6.2.4

Default Clock Source

The device is shipped with CKSEL = "0010", SUT = "10", and CKDIV8 programmed. The default

clock source is therefore the internal RC oscillator running at 8.0 MHz with the longest start-up

time and an initial system clock prescale setting of 8, resulting in a 1 MHz system clock. The

default setting ensures every user can make the desired clock source setting using any available

programming interface.

Table 6-5.

Start-up times for Internal Calibrated RC Oscillator Clock Selection

SUT1..0

Start-up Time

from Power-down

Additional Delay from

Reset (V

CC = 5.0V)

Recommended Usage

6 CK

14CK(1)

BOD enabled

6 CK

14CK + 4 ms

Fast rising power

10(2)

6 CK

14CK + 64 ms

Slowly rising power

Reserved

Table 6-6.

128 kHz Internal Oscillator Operating Modes

CKSEL3..0

Nominal Frequency

0011

128 kHz

Table 6-7.

Start-up Times for the 128 kHz Internal Oscillator

SUT1..0

Start-up Time

from Power-down

Additional Delay

from Reset

Recommended Usage

6 CK

14CK(1)

BOD enabled

6 CK

14CK + 4 ms

Fast rising power

6 CK

14CK + 64 ms

Slowly rising power

Reserved

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