Rainbow Electronics ATtiny43U - Manual (Page 26)

26
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.
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
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
00 6 CK 14CK (1) BOD enabled
01 6 CK 14CK + 4 ms Fast rising power
10 (2) 6 CK 14CK + 64 ms Slowly rising power
11 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
00 6 CK 14CK (1) BOD enabled
01 6 CK 14CK + 4 ms Fast rising power
10 6 CK 14CK + 64 ms Slowly rising power
11 Reserved