ATmega48 datasheet(106/340 Pages) ATMEL

106 / 340 page

106

7530H–AVR–02/09

ATmega48/88/168 Automotive

Figure 14-1. 16-bit Timer/Counter Block Diagram(1)

Note:

1. Refer to Figure 1-1 on page 2,

Table 10-3 on page 70 and Table 10-9 on page 77 for

Timer/Counter1 pin placement and description.

14.1.1

Registers

The Timer/Counter (TCNT1), Output Compare Registers (OCR1A/B), and Input Capture Regis-

ter (ICR1) 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 107. The Timer/Counter Control Registers (TCCR1A/B) are 8-bit registers and have no

CPU access restrictions. Interrupt requests (abbreviated to Int.Req. in the figure) signals are all

visible in the Timer Interrupt Flag Register (TIFR1). All interrupts are individually masked with

the Timer Interrupt Mask Register (TIMSK1). TIFR1 and TIMSK1 are not shown in the figure.

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

the T1 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

T1).

Clock Select

Timer/Counter

OCRnA

OCRnB

ICRn

TCNTn

Waveform

Generation

Waveform

Generation

OCnA

OCnB

Noise

Canceler

ICPn

Fixed

TOP

Values

Edge

Detector

Control Logic

= 0

TOP

BOTTOM

Count

Clear

Direction

TOVn

(Int.Req.)

OCnA

(Int.Req.)

OCnB

(Int.Req.)

ICFn (Int.Req.)

TCCRnA

TCCRnB

( From Analog

Comparator Ouput )

Edge

Detector

( From Prescaler )

clk

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