AT90PWM3 datasheet(103/361 Pages) ATMEL

103 / 361 page

103

4317J–AVR–08/10

AT90PWM2/3/2B/3B

Figure 15-1. 16-bit Timer/Counter Block Diagram

(1)

Note:

1. Refer to

Table on page 4 for Timer/Counter1 pin placement and description.

15.1.1

Registers

The Timer/Counter (TCNTn), Output Compare Registers (OCRnx), and Input Capture 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 “Accessing 16-bit Registers” on page

104. The Timer/Counter Control Registers (TCCRnx) 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 (TIFRn). All interrupts are individually masked with the Timer

Interrupt Mask Register (TIMSKn). TIFRn and TIMSKn are not shown in the figure.

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 (OCRnx) 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 (OCnx). See “Output Compare

Units” on page 110. The compare match event will also set the Compare Match Flag (OCFnx)

which can be used to generate an Output Compare interrupt request.

Clock Select

Timer/Counter

OCRnA

OCRnB

ICRn

TCNTn

Waveform

Generation

Waveform

Generation

OCnA

OCnB

Noise

Canceler

ICPnB

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

Edge

Detector

( From Prescaler )

clk

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