AT90SCR100 datasheet(154/433 Pages) ATMEL

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TPR0327AY–SMS–30Jan09

AT90SCR100

• Bit 0 – TOV2 : Timer/Counter2 Overflow Flag

The TOV2 bit is set (one) when an overflow occurs in Timer/Counter2. TOV2 is cleared by hard-

ware when executing the corresponding interrupt handling vector. Alternatively, TOV2 is cleared

by writing a logic one to the flag. When the SREG I-bit, TOIE2A (Timer/Counter2 Overflow Inter-

rupt Enable), and TOV2 are set (one), the Timer/Counter2 Overflow interrupt is executed. In

PWM mode, this bit is set when Timer/Counter2 changes counting direction at 0x00.

13.4

Timer/Counter Prescaler

Figure 13-36.

Prescaler for Timer/Counter2

The clock source for Timer/Counter2 is named clkT2S. clkT2S is by default connected to the main

system I/O clock clkI

O. By setting the AS2 bit in ASSR, Timer/Counter2 is asynchronously

clocked from the TOSC1 pin. This enables use of Timer/Counter2 as a Real Time Counter

(RTC). When AS2 is set, pins TOSC1 and TOSC2 are disconnected from Port C. A crystal can

then be connected between the TOSC1 and TOSC2 pins to serve as an independent clock

source for Timer/Counter2. The Oscillator is optimized for use with a 32.768 kHz crystal. By set-

ting the EXCLK bit in the ASSR, a 32 kHz external clock can be applied. See “ASSR –

Asynchronous Status Register” on page 150 for details.

For Timer/Counter2, the possible prescaled selections are: clkT2S/8, clkT2S/32, clkT2S/64,

clkT2S/128, clkT2S/256, and clkT2S/1024. Additionally, clkT2S as well as 0 (stop) may be selected.

Setting the PSRASY bit in GTCCR resets the prescaler. This allows the user to operate with a

predictable prescaler.

10-BIT T/C PRESCALER

TIMER/COUNTER2 CLOCK SOURCE

clk

I/O

clk

T2S

TOSC1

AS2

CS20

CS21

CS22

PSRASY

Clear

clk

AT90SCR100 Datasheet(PDF) 154 Page - ATMEL Corporation