ATmega644P Atmel Corporation, ATmega644P Datasheet - Page 37

• Manufacturer Part Number: ATmega644P
• Manufacturer: Atmel Corporation

Specifications of ATmega644P

• Flash (kbytes): 64 Kbytes
• Pin Count: 44
• Max. Operating Frequency: 20 MHz
• Cpu: 8-bit AVR
• # Of Touch Channels: 16
• Hardware Qtouch Acquisition: No
• Max I/o Pins: 32
• Ext Interrupts: 32
• Usb Speed: No
• Usb Interface: No
• Spi: 3
• Twi (i2c): 1
• Uart: 2
• Graphic Lcd: No
• Video Decoder: No
• Camera Interface: No
• Adc Channels: 8
• Adc Resolution (bits): 10
• Adc Speed (ksps): 15
• Analog Comparators: 1
• Resistive Touch Screen: No
• Temp. Sensor: No
• Crypto Engine: No
• Sram (kbytes): 4
• Eeprom (bytes): 2048
• Self Program Memory: YES
• Dram Memory: No
• Nand Interface: No
• Picopower: Yes
• Temp. Range (deg C): -40 to 85
• I/o Supply Class: 1.8 to 5.5
• Operating Voltage (vcc): 1.8 to 5.5
• Fpu: No
• Mpu / Mmu: no / no
• Timers: 3
• Output Compare Channels: 6
• Input Capture Channels: 1
• Pwm Channels: 6
• 32khz Rtc: Yes
• Calibrated Rc Oscillator: Yes

6.7
6.8
8011O–AVR–07/10
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 6-12.
Note:
When this clock source is selected, start-up times are determined by the SUT Fuses as shown in
Table
Table 6-13.
To drive the device from an external clock source, XTAL1 should be driven as shown in
6-3. To run the device on an external clock, the CKSEL Fuses must be programmed to “0000”.
Figure 6-3.
When this clock source is selected, start-up times are determined by the SUT Fuses as shown in
Table
Table 6-14.
BOD enabled
Fast rising power
Slowly rising power
Power Conditions
6-13.
6-15.
1. Note that the 128 kHz oscillator is a very low power clock source, and is not designed for high
accuracy.
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 MHz
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
(2)
Additional Delay from
6-12.
14CK + 64 ms
14CK + 4 ms
Reset
14CK
CKSEL3..0
CKSEL3..0
0011
0000
SUT1..0
00
01
10
11
Figure
37