ATMEGA640 datasheet(138/449 Pages) ATMEL

138 / 449 page

138

ATmega640/1280/1281/2560/2561

2549K–AVR–01/07

Figure 48. 16-bit Timer/Counter Block Diagram

(1)

Note:

1. Refer to Figure 1 on page 2, Table 41 on page 92, and Table 47 on page 96 for

Timer/Counter1 and 3 and 3 pin placement and description.

Registers

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

ture Register (ICRn) are all 16-bit registers. Special procedures must be followed when

accessing the 16-bit registers. These procedures are described in the section “Access-

ing 16-bit Registers” on page 139. 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 (TIFRn). All interrupts

are individually masked with the Timer Interrupt Mask Register (TIMSKn). TIFRn and

TIMSKn 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

Generator to generate a PWM or variable frequency output on the Output Compare pin

(OCnA/B/C). See “Output Compare Units” on page 146.. The compare match event will

ICFn (Int.Req.)

TOVn

(Int.Req.)

Clock Select

Timer/Counter

ICRn

TCNTn

Waveform

Generation

Waveform

Generation

Waveform

Generation

OCnA

OCnB

OCnC

Noise

Canceler

ICPn

Fixed

TOP

Values

Edge

Detector

Control Logic

= 0

TOP

BOTTOM

Count

Clear

Direction

OCFnA

(Int.Req.)

OCFnB

(Int.Req.)

OCFnC

(Int.Req.)

TCCRnA

TCCRnB

TCCRnC

( From Analog

Comparator Ouput )

Edge

Detector

( From Prescaler )

TCLK

OCRnC

OCRnB

OCRnA

ATMEGA640 Datasheet(PDF) 138 Page - ATMEL Corporation

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