ATtiny2313A/4313

12.2.3Compatibility

The 16-bit Timer/Counter has been updated and improved from previous versions of the 16-bit AVR Timer/Counter. This 16-bit Timer/Counter is fully compatible with the earlier version regarding:

•All 16-bit Timer/Counter related I/O Register address locations, including Timer Interrupt Registers.

•Bit locations inside all 16-bit Timer/Counter Registers, including Timer Interrupt Registers.

•Interrupt Vectors.

The following control bits have changed name, but have same functionality and register location:

•PWM10 is changed to WGM10.

•PWM11 is changed to WGM11.

•CTC1 is changed to WGM12.

The following bits are added to the 16-bit Timer/Counter Control Registers:

•FOC1A and FOC1B are added to TCCR1A.

•WGM13 is added to TCCR1B.

The 16-bit Timer/Counter has improvements that will affect the compatibility in some special cases.

12.3Timer/Counter Clock Sources

The Timer/Counter can be clocked by an internal or an external clock source. The clock source is selected by the Clock Select logic which is controlled by the Clock Select (CS12:0) bits located in the Timer/Counter control Register B (TCCR1B). For details on clock sources and prescaler, see “Timer/Counter0 and Timer/Counter1 Prescalers” on page 118.

12.4Counter Unit

The main part of the 16-bit Timer/Counter is the programmable 16-bit bi-directional counter unit. Figure 12-2 shows a block diagram of the counter and its surroundings.

Figure 12-2. Counter Unit Block Diagram

DATA BUS (8-bit)

TOVn

(Int.Req.)

TEMP (8-bit)

Clock Select

Count

Edge

Tn

TCNTnH (8-bit)

TCNTnL (8-bit)

Clear

Control Logic

clkTn

Detector

TCNTn (16-bit Counter)

Direction

( From Prescaler )

TOP

BOTTOM

Signal description (internal signals):

Count	Increment or decrement TCNT1 by 1.
Direction	Select between increment and decrement.
Clear	Clear TCNT1 (set all bits to zero).

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8246B–AVR–09/11