AT90CAN128
Table 8. Start-up Times for the Oscillator Clock Selection
Start-up Time from
Power-down and
Power-save
Additional Delay
from Reset
CKSEL0 SUT1..0
(VCC = 5.0V)
Recommended Usage
0
0
0
0
1
00
01
10
11
00
01
10
11
258 CK(1)
258 CK(1)
1K CK(2)
1K CK(2)
1K CK(2)
16K CK
16K CK
16K CK
14CK + 4.1 ms
14CK + 65 ms
14CK
Ceramic resonator, fast
rising power
Ceramic resonator,
slowly rising power
Ceramic resonator,
BOD enabled
14CK + 4.1 ms
14CK + 65 ms
14CK
Ceramic resonator, fast
rising power
Ceramic resonator,
slowly rising power
Crystal Oscillator, BOD
enabled
1
1
1
14CK + 4.1 ms
14CK + 65 ms
Crystal Oscillator, fast
rising power
Crystal Oscillator,
slowly rising power
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 21.
Figure 21. Low-frequency Crystal Oscillator Connections
12 - 22 pF
XTAL2
32.768 KHz
XTAL1
12 - 22 pF
GND
12-22 pF capacitors may be necessary if the parasitic impedance (pads, wires & PCB)
is very low.
37
4250E–CAN–12/04
ATMEL [ ATMEL ]
