ATMEGA644A-PU Atmel, ATMEGA644A-PU Datasheet - Page 30

• Manufacturer Part Number: ATMEGA644A-PU
• Description: IC MCU AVR 64K FLASH 40PDIP
• Manufacturer: Atmel
• Series: AVR® ATmegar

Specifications of ATMEGA644A-PU

• 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: 40-DIP (0.600", 15.24mm)
• Processor Series: ATmega
• Core: AVR
• Data Bus Width: 8 bit
• Data Ram Size: 4 KB
• Interface Type: JTAG, TWI, SPI, USART
• Maximum Clock Frequency: 20 MHz
• Number Of Programmable I/os: 32
• Number Of Timers: 3
• Operating Supply Voltage: 3.3 V
• Maximum Operating Temperature: + 85 C
• Mounting Style: Through Hole
• Minimum Operating Temperature: - 40 C
• Operating Temperature Range: - 40 C to + 85 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

8. System Clock and Clock Options
8.1
8.1.1
8.1.2
8272A–AVR–01/10
Clock Systems and their Distribution
CPU Clock – clk
I/O Clock – clk
I/O
Figure 8-1
need not be active at a given time. In order to reduce power consumption, the clocks to modules
not being used can be halted by using different sleep modes, as described in
ment and Sleep Modes” on page
Figure 8-1.
The CPU clock is routed to parts of the system concerned with operation of the AVR core.
Examples of such modules are the General Purpose Register File, the Status Register and the
data memory holding the Stack Pointer. Halting the CPU clock inhibits the core from performing
general operations and calculations.
The I/O clock is used by the majority of the I/O modules, like Timer/Counters, SPI, and USART.
The I/O clock is also used by the External Interrupt module, but note that some external inter-
rupts are detected by asynchronous logic, allowing such interrupts to be detected even if the I/O
clock is halted. Also note that start condition detection in the USI module is carried out asynchro-
nously when clk
164A/164PA/324A/324PA/644A/644PA/1284/1284P
CPU
presents the principal clock systems in the AVR and their distribution. All of the clocks
Asynchronous
Timer/Counter
Timer/Counter
Oscillator
Clock Distribution
I/O
is halted, TWI address recognition in all sleep modes.
General I/O
Modules
External Clock
clk
clk
ASY
I/O
43. The clock systems are detailed below.
System Clock
Control Unit
AVR Clock
Multiplexer
Prescaler
Clock
ADC
clk
Source clock
Oscillator
ADC
Crystal
CPU Core
clk
clk
Reset Logic
CPU
FLASH
Crystal Oscillator
Watchdog clock
Low-frequency
Watchdog Timer
RAM
Watchdog
Oscillator
Calibrated RC
Flash and
EEPROM
Oscillator
”Power Manage-
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