ATmega32A Datasheet - Sunrom Technologies

ATmega32AFigure 8-4.External Clock Drive ConfigurationEXTERNALCLOCKSIGNALWhen this clock source is selected, start-up times are determined by the SUT fuses as shown inTable 8-10.Table 8-10.SUT1:0Start-up Times for the External Clock SelectionStart-up Time fromPower-down andPower-saveAdditional Delayfrom Reset(V CC = 5.0V) Recommended Usage00 6 CK – BOD enabled01 6 CK 4.1ms Fast rising power10 6 CK 65ms Slowly rising power11 ReservedWhen applying an external clock, it is required to avoid sudden changes in the applied clock frequencyto ensure stable operation of the MCU. A variation in frequency of more than 2% fromone clock cycle to the next can lead to unpredictable behavior. It is required to ensure that theMCU is kept in reset during such changes in the clock frequency.8.9 Timer/Counter OscillatorFor AVR microcontrollers with Timer/Counter Oscillator pins (TOSC1 and TOSC2), the crystal isconnected directly between the pins. No external capacitors are needed. The Oscillator is optimizedfor use with a 32.768kHz watch crystal. Applying an external clock source to TOSC1 isnot recommended.Note:The Timer/Counter Oscillator uses the same type of crystal oscillator as Low-Frequency Oscillatorand the internal capacitors have the same nominal value of 36pF.8155C–AVR–02/1131