ATMEGA644P-20MQ Atmel, ATMEGA644P-20MQ Datasheet - Page 32

• Manufacturer Part Number: ATMEGA644P-20MQ
• Description: MCU AVR 64K FLASH 20MHZ 44-QFN
• Manufacturer: Atmel
• Series: AVR® ATmegar

Specifications of ATMEGA644P-20MQ

• Core Processor: AVR
• Core Size: 8-Bit
• Speed: 20MHz
• Connectivity: I²C, SPI, UART/USART
• Peripherals: Brown-out Detect/Reset, POR, PWM, WDT
• Number Of I /o: 32
• Program Memory Size: 64KB (32K x 16)
• Program Memory Type: FLASH
• Eeprom Size: 2K x 8
• Ram Size: 4K x 8
• Voltage - Supply (vcc/vdd): 2.7 V ~ 5.5 V
• Data Converters: A/D 8x10b
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 44-VQFN Exposed Pad
• For Use With: ATSTK600 - DEV KIT FOR AVR/AVR32
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

6.3
8011O–AVR–07/10
Low Power Crystal Oscillator
This Crystal Oscillator is a low power oscillator, with reduced voltage swing on the XTAL2 out-
put. It gives the lowest power consumption, but is not capable of driving other clock inputs, and
may be more susceptible to noise in noisy environments. In these cases, refer to the
Crystal Oscillator” on page
Some initial guidelines for choosing capacitors for use with crystals are given in
crystal should be connected as described in
The Low Power Oscillator can operate in three different modes, each optimized for a specific fre-
quency range. The operating mode is selected by the fuses CKSEL3..1 as shown in
Table 6-3.
Notes:
The CKSEL0 Fuse together with the SUT1..0 Fuses select the start-up times as shown in
6-4.
Table 6-4.
Oscillator Source /
Power Conditions
Ceramic resonator, fast
rising power
Ceramic resonator, slowly
rising power
Ceramic resonator, BOD
enabled
Ceramic resonator, fast
rising power
Ceramic resonator, slowly
rising power
Frequency Range (MHz)
1. If 8 MHz frequency exceeds the specification of the device (depends on V
2. This is the recommended CKSEL settings for the different frequency ranges.
3. This option should not be used with crystals, only with ceramic resonators.
Fuse can be programmed in order to divide the internal frequency by 8. It must be ensured
that the resulting divided clock meets the frequency specification of the device.
8.0 - 16.0
0.4 - 0.9
0.9 - 3.0
3.0 - 8.0
Low Power Crystal Oscillator Operating Modes
Start-up Times for the Low Power Crystal Oscillator Clock Selection
33.
Start-up Time from
Power-down and
Power-save
258 CK
258 CK
1K CK
1K CK
1K CK
CKSEL3..1
100
101
110
111
”Clock Source Connections” on page
(3)
(2)
ATmega164P/324P/644P
Additional Delay
14CK + 4.1 ms
14CK + 4.1 ms
Recommended Range for Capacitors C1
14CK + 65 ms
14CK + 65 ms
(V
from Reset
CC
14CK
= 5.0V)
(1)
(2)
(1)
(2)
(1)
(2)
and C2 (pF)
12 - 22
12 - 22
12 - 22
–
CKSEL0
CC
0
0
0
0
1
), the CKDIV8
Table
31.
Table
”Full Swing
SUT1..0
6-3. The
00
01
10
11
00
Table
6-3.
32