
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
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
Figure8-4 on page 33. To run the device on an external clock, the CKSEL Fuses must be programmed
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 8-13.
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
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 (VCC = 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