ATmega649 Atmel Corporation, ATmega649 Datasheet - Page 151
![no-image](/images/manufacturer_photos/0/0/79/atmel_corporation_sml.jpg)
ATmega649
Manufacturer Part Number
ATmega649
Description
Manufacturer
Atmel Corporation
Specifications of ATmega649
Flash (kbytes)
64 Kbytes
Pin Count
64
Max. Operating Frequency
16 MHz
Cpu
8-bit AVR
# Of Touch Channels
16
Hardware Qtouch Acquisition
No
Max I/o Pins
54
Ext Interrupts
17
Usb Speed
No
Usb Interface
No
Spi
2
Twi (i2c)
1
Uart
1
Segment Lcd
100
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
No
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
4
Input Capture Channels
1
Pwm Channels
4
32khz Rtc
Yes
Calibrated Rc Oscillator
Yes
Available stocks
Company
Part Number
Manufacturer
Quantity
Price
Part Number:
ATmega649-16AU
Manufacturer:
ATMEL/爱特梅尔
Quantity:
20 000
Company:
Part Number:
ATmega649-16MU
Manufacturer:
Atmel
Quantity:
135
Part Number:
ATmega6490-16AI
Manufacturer:
ATMEL/爱特梅尔
Quantity:
20 000
Company:
Part Number:
ATmega6490-16AU
Manufacturer:
Atmel
Quantity:
135
Company:
Part Number:
ATmega6490-16AUR
Manufacturer:
Atmel
Quantity:
1 500
Company:
Part Number:
ATmega6490A-AU
Manufacturer:
Atmel
Quantity:
1 250
Company:
Part Number:
ATmega6490A-AUR
Manufacturer:
Maxim
Quantity:
43
17.9
2552K–AVR–04/11
Asynchronous Operation of Timer/Counter2
When Timer/Counter2 operates asynchronously, some considerations must be taken.
•
•
•
•
•
•
•
Warning: When switching between asynchronous and synchronous clocking of
Timer/Counter2, the Timer Registers TCNT2, OCR2A, and TCCR2A might be corrupted. A
safe procedure for switching clock source is:
1. Disable the Timer/Counter2 interrupts by clearing OCIE2A and TOIE2.
2. Select clock source by setting AS2 as appropriate.
3. Write new values to TCNT2, OCR2A, and TCCR2A.
4. To switch to asynchronous operation: Wait for TCN2UB, OCR2UB, and TCR2UB.
5. Clear the Timer/Counter2 Interrupt Flags.
6. Enable interrupts, if needed.
The CPU main clock frequency must be more than four times the Oscillator frequency.
When writing to one of the registers TCNT2, OCR2A, or TCCR2A, the value is transferred to
a temporary register, and latched after two positive edges on TOSC1. The user should not
write a new value before the contents of the temporary register have been transferred to its
destination. Each of the three mentioned registers have their individual temporary register,
which means that e.g. writing to TCNT2 does not disturb an OCR2A write in progress. To
detect that a transfer to the destination register has taken place, the Asynchronous Status
Register – ASSR has been implemented.
When entering Power-save or ADC Noise Reduction mode after having written to TCNT2,
OCR2A, or TCCR2A, the user must wait until the written register has been updated if
Timer/Counter2 is used to wake up the device. Otherwise, the MCU will enter sleep mode
before the changes are effective. This is particularly important if the Output Compare2
interrupt is used to wake up the device, since the Output Compare function is disabled
during writing to OCR2A or TCNT2. If the write cycle is not finished, and the MCU enters
sleep mode before the OCR2UB bit returns to zero, the device will never receive a compare
match interrupt, and the MCU will not wake up.
If Timer/Counter2 is used to wake the device up from Power-save or ADC Noise Reduction
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:
1. Write a value to TCCR2A, TCNT2, or OCR2A.
2. Wait until the corresponding Update Busy Flag in ASSR returns to zero.
3. Enter Power-save or ADC Noise Reduction mode.
When the asynchronous operation is selected, the 32.768kHz Oscillator for Timer/Counter2
is 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.
Description of wake up from Power-save or ADC Noise Reduction mode when the timer is
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
ATmega329/3290/649/6490
151