A000003 Arduino, A000003 Datasheet - Page 150
A000003
Manufacturer Part Number
A000003
Description
MCU, MPU & DSP Development Tools MINI
Manufacturer
Arduino
Series
-r
Type
MCUr
Specifications of A000003
Processor To Be Evaluated
Atmega328
Processor Series
ATmega
Data Bus Width
8 bit
Interface Type
USB, RS-232
Operating Supply Voltage
7 V to 9 V
Contents
Board
Lead Free Status / Rohs Status
Lead free / RoHS Compliant
For Use With/related Products
ATmega168
- Current page: 150 of 378
- Download datasheet (8Mb)
17.9
150
Asynchronous Operation of Timer/Counter2
ATmega48/88/168
When Timer/Counter2 operates asynchronously, some considerations must be taken.
• Warning: When switching between asynchronous and synchronous clocking of
• The CPU main clock frequency must be more than four times the Oscillator frequency.
• When writing to one of the registers TCNT2, OCR2x, or TCCR2x, the value is transferred to a
• When entering Power-save or ADC Noise Reduction mode after having written to TCNT2,
• If Timer/Counter2 is used to wake the device up from Power-save or ADC Noise Reduction
• When the asynchronous operation is selected, the 32.768 kHz Oscillator for Timer/Counter2 is
Timer/Counter2, the Timer Registers TCNT2, OCR2x, and TCCR2x might be corrupted. A safe
procedure for switching clock source is:
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 five mentioned registers have their individual temporary register, which
means that, for example, writing to TCNT2 does not disturb an OCR2x write in progress. To
detect that a transfer to the destination register has taken place, the Asynchronous Status
Register – ASSR has been implemented.
OCR2x, or TCCR2x, 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 any of the Output Compare2
interrupt is used to wake up the device, since the Output Compare function is disabled during
writing to OCR2x or TCNT2. If the write cycle is not finished, and the MCU enters sleep mode
before the corresponding OCR2xUB bit returns to zero, the device will never receive a
compare match interrupt, and the MCU will not wake up.
mode, precautions must be taken if the user wants to re-enter one of these modes: If re-
entering sleep mode within the TOSC1 cycle, the interrupt will immidiately occur and the
device wake up again. The result is multiple interrupts and wake-ups within one TOSC1 cycle
from the first interrupt. 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:
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.
a. Disable the Timer/Counter2 interrupts by clearing OCIE2x and TOIE2.
b. Select clock source by setting AS2 as appropriate.
c. Write new values to TCNT2, OCR2x, and TCCR2x.
d. To switch to asynchronous operation: Wait for TCN2xUB, OCR2xUB, and TCR2xUB.
e. Clear the Timer/Counter2 Interrupt Flags.
f.
a. Write a value to TCCR2x, TCNT2, or OCR2x.
b. Wait until the corresponding Update Busy Flag in ASSR returns to zero.
c. Enter Power-save or ADC Noise Reduction mode.
Enable interrupts, if needed.
2545S–AVR–07/10
Related parts for A000003
Image
Part Number
Description
Manufacturer
Datasheet
Request
R
Part Number:
Description:
Daughter Cards & OEM Boards ARDUINO UNO PROTO PCB REV 3
Manufacturer:
Arduino
Part Number:
Description:
Daughter Cards & OEM Boards ARDUINO SHIELD PROTO KIT REV 3
Manufacturer:
Arduino
Part Number:
Description:
Daughter Cards & OEM Boards ARDUINO MEGA PROTO KIT REV 3
Manufacturer:
Arduino
Part Number:
Description:
Daughter Cards & OEM Boards ARDUINO MEGA PROTO PCB REV 3
Manufacturer:
Arduino
Part Number:
Description:
Development Boards & Kits - AVR ARDUINO STARTER KIT W/ UNO REV3
Manufacturer:
Arduino
Part Number:
Description:
RF Development Tools ARDUINO SHIELD WIRELESS PROTO
Manufacturer:
Arduino
Datasheet:
Part Number:
Description:
RF Development Tools ARDUINO SHIELD WIRELESS WITH SD
Manufacturer:
Arduino
Datasheet:
Part Number:
Description:
Development Software Getting started w/Arduino
Manufacturer:
Arduino
Part Number:
Description:
Ethernet Modules & Development Tools Ethernet Shield for Arduino
Manufacturer:
Arduino
Part Number:
Description:
MCU, MPU & DSP Development Tools LilyPad Arduino Main Board
Manufacturer:
Arduino
Part Number:
Description:
ARDUINO NANO Board
Manufacturer:
Arduino
Datasheet:
Part Number:
Description:
Ethernet Modules & Development Tools ETHERNET SHEILD PoE FOR ARDUINO
Manufacturer:
Arduino
Datasheet:
Part Number:
Description:
ATMEGA328 MCU IC W/ Arduino UNO Bootloader
Manufacturer:
Arduino
Datasheet:
Part Number:
Description:
Memory Cards MICRO SD CARD 1GB WITH SD ADAPTER
Manufacturer:
Arduino