(1) Description of TIMER/COUNTER 0 Timer/Counter Clock Sources The Timer/Counter can be clocked by an internal synchronous or an external asynchronous clock source. The clock source clkto is by default equal to the MCU clock, clkvo When the A bit in the ASSR Register is written to logic one, the clock source is taken from the Timer/Counter Oscillator connected to TOSC1 and TOSC2. Timer/Counter Oscillator microcontrollers with Timer/Counter Oscilator pins (TOSC1 and TOSC2), the crystal is connected directly between the pins. No external capacitors are needed. The Oscillator is opti- mized for use with a 32.768 kHz watch crystal. Applying an external clock source to TOSC1 is not recommended. Figure 35. Counter Unit Block Diagram DATA BUS TOVn (Int.Req) count clear direction TIC Oscillator Control Logic Prascaler TCNTO clko bottom top (1) Description of TIMER/COUNTER 0 Timer/Counter Clock Sources The Timer/Counter can be clocked by an internal synchronous or an external asynchronous clock source. The clock source clkto is by default equal to the MCU clock, clkvo When the A bit in the ASSR Register is written to logic one, the clock source is taken from the Timer/Counter Oscillator connected to TOSC1 and TOSC2. Timer/Counter Oscillator microcontrollers with Timer/Counter Oscilator pins (TOSC1 and TOSC2), the crystal is connected directly between the pins. No external capacitors are needed. The Oscillator is opti- mized for use with a 32.768 kHz watch crystal. Applying an external clock source to TOSC1 is not recommended. Figure 35. Counter Unit Block Diagram DATA BUS TOVn (Int.Req) count clear direction TIC Oscillator Control Logic Prascaler TCNTO clko bottom top