ATMEGA8535-16PJ Atmel, ATMEGA8535-16PJ Datasheet - Page 132
![IC MCU AVR 8K 5V 16MHZ 40-DIP](/photos/6/70/67049/453-40-dip_sml.jpg)
ATMEGA8535-16PJ
Manufacturer Part Number
ATMEGA8535-16PJ
Description
IC MCU AVR 8K 5V 16MHZ 40-DIP
Manufacturer
Atmel
Series
AVR® ATmegar
Specifications of ATMEGA8535-16PJ
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)
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
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Asynchronous Operation of
Timer/Counter2
132
ATmega8535(L)
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.
2502K–AVR–10/06
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