Rainbow-electronics ATmega64L Manual de usuario descargar pdf (Pagina 111)

111

ATmega16(L)

2466B–09/01

8-bit Timer/Counter2

with PWM and

Asynchronous

Operation

Timer/Counter2 is a general purpose, single channel, 8-bit Timer/Counter module. The

main features are:

•

Single Channel Counter

• Clear Timer on Compare Match (Auto Reload)

• Glitch-free, Phase Correct Pulse Width Modulator (PWM)

• Frequency Generator

• 10-bit Clock Prescaler

• Overflow and Compare Match Interrupt Sources (TOV2 and OCF2)

• Allows clocking from External 32 kHz Watch Crystal Independent of the I/O Clock

Overview A simplified block diagram of the 8-bit Timer/Counter is shown in Figure 53. For the

actual placement of I/O pins, refer to “Pinouts ATmega16” on page 2. CPU accessible

I/O registers, including I/O bits and I/O pins, are shown in bold. The device-specific I/O

page 121.

Figure 53. 8-bit Timer/Counter Block Diagram

Registers The Timer/Counter (TCNT2) and Output Compare Register (OCR2) are 8-bit registers.

Interrupt request (shorten as Int.Req.) signals are all visible in the Timer Interrupt Flag

ister (TIMSK). TIFR and 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 asynchronously

clocked from the TOSC1/2 pins, as detailed later in this section. The asynchronous

operation is controlled by the Asynchronous Status Register (ASSR). The Clock Select

logic block controls which clock source the Timer/Counter uses to increment (or decre-

ment) 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

Timer/Counter

DATA B U S

TCNTn

Waveform

Generation

OCn

= 0

Control Logic

= 0xFF

TOPBOTTOM

count

clear

direction

TOVn

(Int.Req.)

OCn

(Int.Req.)

Synchronization Unit

OCRn

TCCRn

ASSRn

Status flags

clk

I/O

clk

ASY

Synchronized Status flags

asynchronous mode

select (ASn)

TOSC1

T/C

Oscillator

TOSC2

Prescaler

clk

I/O

1 2 ... 106 107 108 109 110 111 112 113 114 115 116 ... 297 298

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