ATmega64A
Table 8-3.
Start-up Times for the Crystal Oscillator Clock Selection
Start-up Time from
Power-down and
Power-save
Additional Delay
from Reset
CKSEL0
SUT1:0
(VCC = 5.0V)
Recommended Usage
Ceramic resonator, fast
rising power
0
00
258 CK(1)
258 CK(1)
1K CK(2)
1K CK(2)
1K CK(2)
16K CK
16K CK
16K CK
4.1 ms
65 ms
–
Ceramic resonator, slowly
rising power
0
0
0
1
1
1
1
01
10
11
00
01
10
11
Ceramic resonator, BOD
enabled
Ceramic resonator, fast
rising power
4.1 ms
65 ms
–
Ceramic resonator, slowly
rising power
Crystal Oscillator, BOD
enabled
Crystal Oscillator, fast
rising power
4.1 ms
65 ms
Crystal Oscillator, slowly
rising power
Notes: 1. These options should only be used when not operating close to the maximum frequency 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 frequency stability
at start-up. They can also be used with crystals when not operating close to the maximum fre-
quency of the device, and if frequency stability at start-up is not important for the application.
8.5
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 “1001”. The crystal should be con-
nected as shown in Figure 8-2. By programming the CKOPT Fuse, the user can enable internal
capacitors on XTAL1 and XTAL2, thereby removing the need for external capacitors. The inter-
nal capacitors have a nominal value of 36 pF.
When this Oscillator is selected, start-up times are determined by the SUT Fuses as shown in
Table 8-4.
Table 8-4.
Start-up Times for the Low-frequency Crystal Oscillator Clock Selection
Start-up Time from
Power-down and
Power-save
Additional Delay from
Reset
SUT1:0
00
(VCC = 5.0V)
Recommended Usage
1K CK(1)
1K CK(1)
32K CK
4.1 ms
65 ms
Fast rising power or BOD enabled
Slowly rising power
01
10
65 ms
Stable frequency at start-up
11
Reserved
Note:
1. These options should only be used if frequency stability at start-up is not important for the
application.
40
8160C–AVR–07/09
ATMEL [ ATMEL ]
