ATMEGA644PV ATMEL [ATMEL Corporation], ATMEGA644PV Datasheet - Page 37

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ATMEGA644PV

Manufacturer Part Number
ATMEGA644PV
Description
8-bit Microcontroller with 16/32/64K Bytes In-System Programmable Flash
Manufacturer
ATMEL [ATMEL Corporation]
Datasheet

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7.7
7.8
8011D–AVR–02/07
128 kHz Internal Oscillator
External Clock
The 128 kHz internal Oscillator is a low power Oscillator providing a clock of 128 kHz. The fre-
quency is nominal at 3V and 25°C. This clock may be select as the system clock by
programming the CKSEL Fuses to “0011” as shown in
Table 7-12.
Note:
When this clock source is selected, start-up times are determined by the SUT Fuses as shown in
Table
Table 7-13.
To drive the device from an external clock source, XTAL1 should be driven as shown in
7-4. To run the device on an external clock, the CKSEL Fuses must be programmed to “0000”.
Figure 7-4.
When this clock source is selected, start-up times are determined by the SUT Fuses as shown in
Table
Table 7-14.
BOD enabled
Fast rising power
Slowly rising power
Power Conditions
7-13.
7-15.
1. The frequency is preliminary value. Actual value is TBD.
128 kHz Internal Oscillator Operating Modes
Start-up Times for the 128 kHz Internal Oscillator
External Clock Drive Configuration
Crystal Oscillator Clock Frequency
Nominal Frequency
Nominal Frequency
0 - 20 kHz
EXTERNAL
128 kHz
SIGNAL
CLOCK
Start-up Time from Power-
down and Power-save
NC
Reserved
6 CK
6 CK
6 CK
ATmega164P/324P/644P
XTAL2
XTAL1
GND
Table
Additional Delay from
7-12.
14CK + 64 ms
14CK + 4 ms
Reset
14CK
CKSEL3..0
CKSEL3..0
0011
0000
SUT1..0
00
01
10
11
Figure
37

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