ATMEGA644A-MU Atmel, ATMEGA644A-MU Datasheet - Page 39
![IC MCU AVR 64K FLASH 44VQFN](/photos/12/13/121316/313-44-qfn_sml.jpg)
ATMEGA644A-MU
Manufacturer Part Number
ATMEGA644A-MU
Description
IC MCU AVR 64K FLASH 44VQFN
Manufacturer
Atmel
Series
AVR® ATmegar
Specifications of ATMEGA644A-MU
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)
1.8 V ~ 5.5 V
Data Converters
A/D 8x10b
Oscillator Type
Internal
Operating Temperature
-40°C ~ 85°C
Package / Case
44-VQFN Exposed Pad
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
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8.9
8.10
8272A–AVR–01/10
Timer/Counter Oscillator
Clock Output Buffer
Table 8-14.
Table 8-15.
When applying an external clock, it is required to avoid sudden changes in the applied clock fre-
quency to ensure stable operation of the MCU. A variation in frequency of more than 2% from
one clock cycle to the next can lead to unpredictable behavior. If changes of more than 2% is
required, ensure that the MCU is kept in Reset during the changes.
Note that the System Clock Prescaler can be used to implement run-time changes of the internal
clock frequency while still ensuring stable operation. Refer to
40
ATmega164A/164PA/324A/324PA/644A/644PA/1284/1284P uses the same type of crystal
oscillator for Low-frequency Crystal Oscillator and Timer/Counter Oscillator. See
quency Crystal Oscillator” on page 35
The device can operate its Timer/Counter2 from an external 32.768 kHz watch crystal or a exter-
nal clock source. See
Applying an external clock source to TOSC1 can be done if EXTCLK in the ASSR Register is
written to logic one. See
uously compared with the counter value (TCNT2). A match can be used to generate an Output
Compare interrupt, or to generate a waveform output on the OC2B pin.” on page 158
description on selecting external clock as input instead of a 32.768 kHz watch crystal.
The device can output the system clock on the CLKO pin. To enable the output, the CKOUT
Fuse has to be programmed. This mode is suitable when the chip clock is used to drive other cir-
cuits on the system. The clock also will be output during reset, and the normal operation of I/O
pin will be overridden when the fuse is programmed. Any clock source, including the internal RC
Oscillator, can be selected when the clock is output on CLKO. If the System Clock Prescaler is
used, it is the divided system clock that is output.
164A/164PA/324A/324PA/644A/644PA/1284/1284P
BOD enabled
Fast rising power
Slowly rising power
for details.
Power Conditions
Crystal Oscillator Clock Frequency
Start-up Times for the External Clock Selection
Nominal Frequency
”Clock Source Connections” on page 32
”The Output Compare Register B contains an 8-bit value that is contin-
0 - 20 MHz
Start-up Time from Power-
down and Power-save
Reserved
for details on the oscillator and crystal requirements.
6 CK
6 CK
6 CK
Additional Delay from
”System Clock Prescaler” on page
Reset (V
for details.
14CK + 4.1 ms
14CK + 65 ms
14CK
CC
CKSEL3..0
= 5.0V)
0000
”Low Fre-
for further
SUT1..0
00
01
10
11
39
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