ATMEGA163-8AI Atmel, ATMEGA163-8AI Datasheet - Page 58

• Manufacturer Part Number: ATMEGA163-8AI
• Description: IC AVR MCU 16K A/D 8MHZ 44TQFP
• Manufacturer: Atmel
• Series: AVR® ATmegar

Specifications of ATMEGA163-8AI

• Core Processor: AVR
• Core Size: 8-Bit
• Speed: 8MHz
• Connectivity: I²C, SPI, UART/USART
• Peripherals: Brown-out Detect/Reset, POR, PWM, WDT
• Number Of I /o: 32
• Program Memory Size: 16KB (8K x 16)
• Program Memory Type: FLASH
• Eeprom Size: 512 x 8
• Ram Size: 1K x 8
• Voltage - Supply (vcc/vdd): 4 V ~ 5.5 V
• Data Converters: A/D 8x10b
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 44-TQFP, 44-VQFP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

Asynchronous Operation of
Timer/Counter2
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ATmega163(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 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 Compare2 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 mode,
precautions must be taken if the user wants to re-enter Power-save mode: The
interrupt logic needs one TOSC1 cycle to be Reset. If the time between wake-up
and re-entering Power-save 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 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 mode.
When the asynchronous operation is selected, the 32.768 kHz Oscillator for
Timer/Counter2 is always running, except in Power-down mode. After a Power-up
Reset or Wake-up from Power-down, 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. The contents of all Timer/Counter2 Registers must be considered
lost after a wake-up from Power-down due to unstable clock signal upon startup.
Description of wake-up from Power-save mode when the Timer is clocked
asynchronously: When the interrupt condition is met, the wake-up process is started
TCR2UB.
1142E–AVR–02/03