Datasheet

33
7810C–AVR–10/12
Atmel ATmega328P [Preliminary]
When this clock source is selected, start-up times are determined by the SUT Fuses as shown in
Table 8-13.
Note: 1. If the RSTDISBL fuse is programmed, this start-up time will be increased to
14CK + 4.1 ms to ensure programming mode can be entered.
8.8 External Clock
To drive the device from an external clock source, XTAL1 should be driven as shown in Figure
8-4 on page 33. To run the device on an external clock, the CKSEL Fuses must be programmed
to “0000” (see Table 8-14).
Figure 8-4. External Clock Drive Configuration
When this clock source is selected, start-up times are determined by the SUT Fuses as shown in
Table 8-15.
Table 8-13. Start-up Times for the 128 kHz Internal Oscillator
Power Conditions
Start-up Time from
Power-down and Power-save
Additional Delay from
Reset SUT1..0
BOD enabled 6 CK 14CK
(1)
00
Fast rising power 6 CK 14CK + 4 ms 01
Slowly rising power 6 CK 14CK + 64 ms 10
Reserved 11
Table 8-14. Crystal Oscillator Clock Frequency
Frequency CKSEL3..0
0 - 16 MHz 0000
Table 8-15. Start-up Times for the External Clock Selection
Power Conditions
Start-up Time from
Power-down and Power-save
Additional Delay from
Reset (V
CC
= 5.0V) SUT1..0
BOD enabled 6 CK 14CK 00
Fast rising power 6 CK 14CK + 4.1 ms 01
Slowly rising power 6 CK 14CK + 65 ms 10
Reserved 11
NC
EXTERNAL
CLOCK
SIGNAL
XTAL2
XTAL1
GND