ATMEGA644P-A15MZ Atmel, ATMEGA644P-A15MZ Datasheet - Page 152

• Manufacturer Part Number: ATMEGA644P-A15MZ
• Description: MCU AVR 64KB FLASH 16MHZ 44QFN
• Manufacturer: Atmel
• Series: AVR® ATmegar

Specifications of ATMEGA644P-A15MZ

• Package / Case: 44-VQFN Exposed Pad
• Voltage - Supply (vcc/vdd): 2.7 V ~ 5.5 V
• Operating Temperature: -40°C ~ 125°C
• Speed: 16MHz
• Number Of I /o: 32
• Eeprom Size: 2K x 8
• Core Processor: AVR
• Program Memory Type: FLASH
• Ram Size: 4K x 8
• Program Memory Size: 64KB (64K x 8)
• Data Converters: A/D 8x10b
• Oscillator Type: Internal
• Peripherals: Brown-out Detect/Reset, POR, PWM, WDT
• Connectivity: I²C, SPI, UART/USART
• Core Size: 8-Bit
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

152
ATmega164P/324P/644P
• If Timer/Counter2 is used to wake the device up from Power-save or ADC Noise Reduction
• When the asynchronous operation is selected, the 32.768 kHz Oscillator for Timer/Counter2 is
• Description of wake up from Power-save or ADC Noise Reduction mode when the timer is
• Reading of the TCNT2 Register shortly after wake-up from Power-save may give an incorrect
• During asynchronous operation, the synchronization of the Interrupt Flags for the
mode, precautions must be taken if the user wants to re-enter one of these modes: The
interrupt logic needs one TOSC1 cycle to be reset. If the time between wake-up and
re-entering sleep mode is less than one TOSC1 cycle, the interrupt will not occur, and the
device will fail to wake up. If the user is in doubt whether the time before re-entering
Power-save or ADC Noise Reduction mode is sufficient, the following algorithm can be used to
ensure that one TOSC1 cycle has elapsed:
always running, except in Power-down and Standby modes. After a Power-up Reset or
wake-up from Power-down or Standby mode, the user should be aware of the fact that this
Oscillator might take as long as one second to stabilize. The user is advised to wait for at least
one second before using Timer/Counter2 after power-up or wake-up from Power-down or
Standby mode. The contents of all Timer/Counter2 Registers must be considered lost after a
wake-up from Power-down or Standby mode due to unstable clock signal upon start-up, no
matter whether the Oscillator is in use or a clock signal is applied to the TOSC1 pin.
clocked asynchronously: When the interrupt condition is met, the wake up process is started
on the following cycle of the timer clock, that is, the timer is always advanced by at least one
before the processor can read the counter value. After wake-up, the MCU is halted for four
cycles, it executes the interrupt routine, and resumes execution from the instruction following
SLEEP.
result. Since TCNT2 is clocked on the asynchronous TOSC clock, reading TCNT2 must be
done through a register synchronized to the internal I/O clock domain. Synchronization takes
place for every rising TOSC1 edge. When waking up from Power-save mode, and the I/O clock
(clk
until the next rising TOSC1 edge. The phase of the TOSC clock after waking up from
Power-save mode is essentially unpredictable, as it depends on the wake-up time. The
recommended procedure for reading TCNT2 is thus as follows:
asynchronous timer takes 3 processor cycles plus one timer cycle. The timer is therefore
advanced by at least one before the processor can read the timer value causing the setting of
the Interrupt Flag. The Output Compare pin is changed on the timer clock and is not
synchronized to the processor clock.
a. Write a value to TCCR2x, TCNT2, or OCR2x.
b. Wait until the corresponding Update Busy Flag in ASSR returns to zero.
c. Enter Power-save or ADC Noise Reduction mode.
a. Write any value to either of the registers OCR2x or TCCR2x.
b. Wait for the corresponding Update Busy Flag to be cleared.
c. Read TCNT2.
I/O
) again becomes active, TCNT2 will read as the previous value (before entering sleep)
7674F–AVR–09/09