ATMEGA8535-16PU Atmel, ATMEGA8535-16PU Datasheet - Page 131

• Manufacturer Part Number: ATMEGA8535-16PU
• Description: IC AVR MCU 8K 16MHZ 5V 40DIP
• Manufacturer: Atmel
• Series: AVR® ATmegar

Specifications of ATMEGA8535-16PU

• Core Processor: AVR
• Core Size: 8-Bit
• Speed: 16MHz
• Connectivity: I²C, SPI, UART/USART
• Peripherals: Brown-out Detect/Reset, POR, PWM, WDT
• Number Of I /o: 32
• Program Memory Size: 8KB (4K x 16)
• Program Memory Type: FLASH
• Eeprom Size: 512 x 8
• Ram Size: 512 x 8
• Voltage - Supply (vcc/vdd): 4.5 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: ATMEGA8x
• Core: AVR8
• Data Bus Width: 8 bit
• Data Ram Size: 512 B
• Interface Type: 2-Wire, SPI, USART
• Maximum Clock Frequency: 16 MHz
• Number Of Programmable I/os: 32
• Number Of Timers: 3
• Operating Supply Voltage: 4.5 V to 5.5 V
• Maximum Operating Temperature: + 85 C
• Mounting Style: Through Hole
• 3rd Party Development Tools: EWAVR, EWAVR-BL
• Development Tools By Supplier: ATAVRDRAGON, ATSTK500, ATSTK600, ATAVRISP2, ATAVRONEKIT
• Minimum Operating Temperature: - 40 C
• On-chip Adc: 10 bit, 8 Channel
• A/d Inputs: 8-Channel, 10-Bit
• Cpu Speed: 16 MIPS
• Eeprom Memory: 512 Bytes
• Input Output: 32
• Interface: SPI/TWI/USART
• Memory Type: Flash
• Number Of Bits: 8
• Package Type: 40-pin PDIP
• Programmable Memory: 8K Bytes
• Timers: 2-8-bit, 1-16-bit
• Voltage, Range: 4.5-5.5 V
• Controller Family/series: AVR MEGA
• No. Of I/o's: 32
• Eeprom Memory Size: 512Byte
• Ram Memory Size: 512Byte
• Rohs Compliant: Yes
• For Use With: ATSTK600 - DEV KIT FOR AVR/AVR32770-1007 - ISP 4PORT ATMEL AVR MCU SPI/JTAGATAVRISP2 - PROGRAMMER AVR IN SYSTEMATSTK500 - PROGRAMMER AVR STARTER KIT
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Asynchronous Operation of
Timer/Counter2
2502G–AVR–04/05
When Timer/Counter2 operates asynchronously, some considerations must be taken.
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Warning: When switching between asynchronous and synchronous clocking of
Timer/Counter2, the timer registers TCNT2, OCR2, and TCCR2 might be corrupted.
A safe procedure for switching clock source is:
1. Disable the Timer/Counter2 interrupts by clearing OCIE2 and TOIE2.
2. Select clock source by setting AS2 as appropriate.
3. Write new values to TCNT2, OCR2, and TCCR2.
4. To switch to asynchronous operation: Wait for TCN2UB, OCR2UB, and
5. Clear the Timer/Counter2 Interrupt Flags.
6. Enable interrupts, if needed.
The Oscillator is optimized for use with a 32.768 kHz watch crystal. Applying an
external clock to the TOSC1 pin may result in incorrect Timer/Counter2 operation.
The CPU main clock frequency must be more than four times the oscillator
frequency.
When writing to one of the registers TCNT2, OCR2, or TCCR2, 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 OCR2 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 Extended Standby mode after having written to
TCNT2, OCR2, or TCCR2, 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 Compare 2 interrupt is used to wake up the device, since the output
compare function is disabled during writing to OCR2 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 Extended
Standby 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 Extended Standby mode is sufficient, the following
algorithm can be used to ensure that one TOSC1 cycle has elapsed:
1. Write a value to TCCR2, TCNT2, or OCR2.
2. Wait until the corresponding Update Busy Flag in ASSR returns to zero.
3. Enter Power-save or Extended Standby mode.
When the asynchronous operation is selected, the 32.768 kHz 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-
TCR2UB.
ATmega8535(L)
131