ATMEGA649A-AU Atmel, ATMEGA649A-AU Datasheet - Page 37

• Manufacturer Part Number: ATMEGA649A-AU
• Description: IC MCU AVR 64K FLASH 64TQFP
• Manufacturer: Atmel
• Series: AVR® ATmegar

Specifications of ATMEGA649A-AU

• Core Processor: AVR
• Core Size: 8-Bit
• Speed: 16MHz
• Connectivity: SPI, UART/USART, USI
• Peripherals: Brown-out Detect/Reset, LCD, POR, PWM, WDT
• Number Of I /o: 54
• 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: 64-TQFP
• Processor Series: ATmega
• Core: AVR
• Data Bus Width: 8 bit
• Data Ram Size: 4 KB
• Interface Type: SPI, USART
• Maximum Clock Frequency: 16 MHz
• Number Of Programmable I/os: 54
• Number Of Timers: 3
• Operating Supply Voltage: 3.3 V
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Minimum Operating Temperature: - 40 C
• Operating Temperature Range: - 40 C to + 85 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

8.9
8.10
8.10.1
8284A–AVR–10/10
Timer/Counter Oscillator
System Clock Prescaler
Switching Time
ATmega169A/169PA/329A/329PA/3290A/3290PA/649A/649P/6490A/6490P uses the same
crystal oscillator for Low-frequency Oscillator and Timer/Counter Oscillator. See
Crystal Oscillator” on page 34
ATmega169A/169PA/329A/329PA/3290A/3290PA/649A/649P/6490A/6490P share the
Timer/Counter Oscillator Pins (TOSC1 and TOSC2) with XTAL1 and XTAL2. When using the
Timer/Counter Oscillator, the system clock needs to be four times the oscillator frequency. Due
to this and the pin sharing, the Timer/Counter Oscillator can only be used when the Calibrated
Internal RC Oscillator is selected as system clock source.
Applying an external clock source to TOSC1 can be done if EXTCLK in the ASSR Register is
written to logic one. See
description on selecting external clock as input instead of a 32.768 kHz watch crystal.
The ATmega169A/169PA/329A/329PA/3290A/3290PA/649A/649P/6490A/6490P system clock
can be divided by setting the Clock Prescale Register – CLKPR. This feature can be used to
decrease power consumption when the requirement for processing power is low. This can be
used with all clock source options, and it will affect the clock frequency of the CPU and all syn-
chronous peripherals. clk
Table 8-14 on page
When switching between prescaler settings, the System Clock Prescaler ensures that no
glitches occur in the clock system and that no intermediate frequency is higher than neither the
clock frequency corresponding to the previous setting, nor the clock frequency corresponding to
the new setting.
The ripple counter that implements the prescaler runs at the frequency of the undivided clock,
which may be faster than the CPU’s clock frequency. Hence, it is not possible to determine the
state of the prescaler – even if it were readable, and the exact time it takes to switch from one
clock division to another cannot be exactly predicted.
From the time the CLKPS values are written, it takes between T1 + T2 and T1 + 2*T2 before the
new clock frequency is active. In this interval, 2 active clock edges are produced. Here, T1 is the
previous clock period, and T2 is the period corresponding to the new prescaler setting.
ATmega169A/169PA/329A/329PA/649A/649P/3290A/3290PA/6490A/6490P
39.
”Asynchronous Operation of Timer/Counter2” on page 158
I/O
, clk
for details on the oscillator and crystal requirements.
ADC
, clk
CPU
, and clk
FLASH
are divided by a factor as shown in
”Low-frequency
for further
37