26
8048C–AVR–02/12
ATtiny43U
When this Oscillator 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 ms to ensure programming mode can be entered.
2.
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
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.
6.2.5
Clock Startup Sequence
Any clock source needs a sufficient V
CC to start oscillating and a minimum number of oscillating
cycles before it can be considered stable.
Table 6-5.
Start-up times for Internal Calibrated RC Oscillator Clock Selection
SUT[1:0]
Start-up Time
from Power-down
Additional Delay from
Reset (V
CC = 5.0V)
Recommended Usage
00
6 CK
BOD enabled
01
6 CK
14CK + 4 ms
Fast rising power
6 CK
14CK + 64 ms
Slowly rising power
11
Reserved
Table 6-6.
128 kHz Internal Oscillator Operating Modes
CKSEL[3:0]
Nominal Frequency
0011
128 kHz
Table 6-7.
Start-up Times for the 128 kHz Internal Oscillator
SUT[1:0]
Start-up Time
from Power-down
Additional Delay
from Reset
Recommended Usage
00
6 CK
BOD enabled
01
6 CK
14CK + 4 ms
Fast rising power
10
6 CK
14CK + 64 ms
Slowly rising power
11
Reserved