ATMEGA8L ATMEL [ATMEL Corporation], ATMEGA8L Datasheet - Page 26

• Manufacturer Part Number: ATMEGA8L
• Description: 8-bit AVR with 8K Bytes In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

Low-frequency Crystal
Oscillator
26
ATmega8(L)
Table 5. Start-up Times for the Crystal Oscillator Clock Selection
Notes:
To use a 32.768 kHz watch crystal as the clock source for the device, the Low-fre-
quency Crystal Oscillator must be selected by setting the CKSEL Fuses to “1001”. The
crystal should be connected as shown in Figure 11. By programming the CKOPT Fuse,
the user can enable internal capacitors on XTAL1 and XTAL2, thereby removing the
need for external capacitors. The internal 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 6.
Table 6. Start-up Times for the Low-frequency Crystal Oscillator Clock Selection
Note:
CKSEL0
SUT1..0
00
01
10
11
0
0
0
0
1
1
1
1
1. These options should only be used when not operating close to the maximum fre-
2. These options are intended for use with ceramic resonators and will ensure fre-
1. These options should only be used if frequency stability at start-up is not important for
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.
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.
the application.
SUT1..0
Start-up Time from
Power-down and
00
01
10
11
00
01
10
11
Power-save
1K CK
1K CK
32K CK
from Power-down
and Power-save
(1)
(1)
Start-up Time
258 CK
258 CK
1K CK
1K CK
1K CK
16K CK
16K CK
16K CK
(2)
(2)
(2)
(1)
(1)
Additional Delay
(V
from Reset
CC
4.1 ms
65 ms
65 ms
= 5.0V)
Additional Delay
Reserved
(V
from Reset
CC
4.1 ms
4.1 ms
4.1 ms
65 ms
65 ms
65 ms
= 5.0V)
–
–
Recommended Usage
Fast rising power or BOD enabled
Slowly rising power
Stable frequency at start-up
Recommended Usage
Ceramic resonator, fast
rising power
Ceramic resonator, slowly
rising power
Ceramic resonator, BOD
enabled
Ceramic resonator, fast
rising power
Ceramic resonator, slowly
rising power
Crystal Oscillator, BOD
enabled
Crystal Oscillator, fast
rising power
Crystal Oscillator, slowly
rising power
2486M–AVR–12/03