Rainbow Electronics Atmega169L - Manual (Page 26)

26
ATmega169V/L
2514A–AVR–08/02
Notes: 1. These options should only be used when not operating close to the maximum fre-
quency of the device, and only if frequency stability at start-up is not important for the
application. These options are not suitable for crystals.
2. These options are intended for use with ceramic resonators and will ensure fre-
quency stability at start-up. They can also be used with crystals when not operating
close to the maximum frequency of the device, and if frequency stability at start-up is
not important for the application.
Low-frequency Crystal
Oscillator To use a 32.768 kHz watch crystal as the clock source for the device, the low-frequency
crystal Oscillator must be selected by setting the CKSEL Fuses to “0100”, “0101”,
“0110”, or “0111”. The crystal should be connected as shown in Figure 12. When this
Oscillator is selected, start-up times are determined by the SUT Fuses as shown in
Table 6 and CKSEL1..0 as shown in Table 7.
Table 5. Start-up Times for the Crystal Oscillator Clock Selection
CKSEL0 SUT1..0
Start-up Time from
Power-down and
Power-save
Additional Delay
from Reset
(V
CC
= 5.0V) Recommended Usage
0 00 258 CK (1) 14CK + 4.1 ms Ceramic resonator, fast
rising power
0 01 258 CK (1) 14CK + 65 ms Ceramic resonator,
slowly rising power
0 10 1K CK (2) 14CK Ceramic resonator,
BOD enabled
0 11 1K CK (2) 14CK + 4.1 ms Ceramic resonator, fast
rising power
1 00 1K CK (2) 14CK + 65 ms Ceramic resonator,
slowly rising power
1
01 16K CK 14CK Crystal Oscillator, BOD
enabled
1
10 16K CK 14CK + 4.1 ms Crystal Oscillator, fast
rising power
1
11 16K CK 14CK + 65 ms Crystal Oscillator,
slowly rising power
Table 6. Start-up Times for the Low-frequency Crystal Oscillator Clock Selection
SUT1..0 Additional Delay from Reset (V
CC
= 5.0V) Recommended Usage
00 14CK Fast rising power or BOD enabled
01 14CK + 4.1 ms Slowly rising power
10 14CK + 65 ms Stable frequency at start-up
11 Reserved