ATmega128 datasheet(113/386 Pages) ATMEL

113 / 386 page

113

2467S–AVR–07/09

ATmega128

Figure 46. 16-bit Timer/Counter Block Diagram

Note:

Refer to Figure 1 on page 2, Table 30 on page 74, and Table 39 on page 81 for Timer/Counter1

and 3 pin placement and description.

Registers

The Timer/Counter (TCNTn), Output Compare Registers (OCRnA/B/C), and Input Capture Reg-

ister (ICRn) are all 16-bit registers. Special procedures must be followed when accessing the 16-

bit registers. These procedures are described in the section “Accessing 16-bit Registers” on

page 115. The Timer/Counter Control Registers (TCCRnA/B/C) are 8-bit registers and have no

CPU access restrictions. Interrupt requests (shorten as Int.Req.) signals are all visible in the

Timer Interrupt Flag Register (TIFR) and Extended Timer Interrupt Flag Register (ETIFR). All

interrupts are individually masked with the Timer Interrupt Mask Register (TIMSK) and Extended

Timer Interrupt Mask Register (ETIMSK). (E)TIFR and (E)TIMSK are not shown in the figure

since these registers are shared by other timer units.

The Timer/Counter can be clocked internally, via the prescaler, or by an external clock source on

the Tn pin. The Clock Select logic block controls which clock source and edge the Timer/Counter

uses to increment (or decrement) its value. The Timer/Counter is inactive when no clock source

is selected. The output from the clock select logic is referred to as the timer clock (clk

Tn).

The double buffered Output Compare Registers (OCRnA/B/C) are compared with the

Timer/Counter value at all time. The result of the compare can be used by the waveform gener-

ator to generate a PWM or variable frequency output on the Output Compare Pin (OCnA/B/C).

ICFx (Int.Req.)

TOVx

(Int.Req.)

Clock Select

Timer/Counter

OCRxA

OCRxB

OCRxC

ICRx

TCNTx

Waveform

Generation

Waveform

Generation

Waveform

Generation

OCxA

OCxB

OCxC

Noise

Canceler

ICPx

Fixed

TOP

Values

Edge

Detector

Control Logic

= 0

TOP

BOTTOM

Count

Clear

Direction

OCFxA

(Int.Req.)

OCFxB

(Int.Req.)

OCFxC

(Int.Req.)

TCCRxA

TCCRxB

TCCRxC

( From Analog

Comparator Ouput )

Edge

Detector

( From Prescaler )

TCLK

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