ATMEGA640 datasheet(178/449 Pages) ATMEL

178 / 449 page

178

ATmega640/1280/1281/2560/2561

2549K–AVR–01/07

Figure 67. Counter Unit Block Diagram

Signal description (internal signals):

count

Increment or decrement TCNT2 by 1.

direction

Selects between increment and decrement.

clear

Clear TCNT2 (set all bits to zero).

clk

Timer/Counter clock, referred to as clk

T2 in the following.

top

Signalizes that TCNT2 has reached maximum value.

bottom

Signalizes that TCNT2 has reached minimum value (zero).

Depending on the mode of operation used, the counter is cleared, incremented, or dec-

remented at each timer clock (clk

T2). clkT2 can be generated from an external or internal

clock source, selected by the Clock Select bits (CS22:0). When no clock source is

selected (CS22:0 = 0) the timer is stopped. However, the TCNT2 value can be accessed

by the CPU, regardless of whether clk

T2 is present or not. A CPU write overrides (has

priority over) all counter clear or count operations.

The counting sequence is determined by the setting of the WGM21 and WGM20 bits

located in the Timer/Counter Control Register (TCCR2A) and the WGM22 located in the

Timer/Counter Control Register B (TCCR2B). There are close connections between

how the counter behaves (counts) and how waveforms are generated on the Output

Compare outputs OC2A and OC2B. For more details about advanced counting

sequences and waveform generation, see “Modes of Operation” on page 179.

The Timer/Counter Overflow Flag (TOV2) is set according to the mode of operation

selected by the WGM22:0 bits. TOV2 can be used for generating a CPU interrupt.

DATA BUS

TCNTn

Control Logic

count

TOVn

(Int.Req.)

top

bottom

direction

clear

TOSC1

T/C

Oscillator

TOSC2

Prescaler

clk

I/O

clk

ATMEGA640 Datasheet(PDF) 178 Page - ATMEL Corporation

ATMEGA640 Datasheet(HTML) 178 Page - ATMEL Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL