Rainbow-electronics ATmega8HVD Manuel d'utilisateur télécharger pdf (Page 76)

8052B–AVR–09/08

ATmega4HVD/8HVD

Figure 16-2. Counter Unit Block Diagram

Signal description (internal signals):

count Increment or decrement TCNTn by 1.

clk

Timer/Counter clock, referred to as clk

in the following.

top Signalize that TCNTn has reached maximum value.

The counter is incremented at each timer clock (clk

) until it passes its TOP value and then

restarts from BOTTOM. The counting sequence is determined by the setting of the WGMn0

bits located in the Timer/Counter Control Register (TCCRnA). For more details about counting

sequences, see ”Timer/Counter Timing Diagrams” on page 81. clk

can be generated from an

external or internal clock source, selected by the Clock Select bits (CSn2:0). When no clock

source is selected (CSn2:0 = 0) the timer is stopped. However, the TCNTn value can be

accessed by the CPU, regardless of whether clk

is present or not. A CPU write overrides

(has priority over) all counter clear or count operations. The Timer/Counter Overflow Flag

(TOVn) is set when the counter reaches the maximum value and it can be used for generating

a CPU interrupt.

16.5 Modes of Operation

The mode of operation is defined by the Timer/Counter Width (TCWn), Input Capture Enable

(ICENn) and the Waveform Generation Mode (WGMn0)bits in ”TCCRnA – Timer/Counter n

Control Register A” on page 86. Table 16-2 on page 76 shows the different Modes of

Operation.

DATA B U S

TCNTn Control Logic

count

TOVn

(Int.Req.)

Clock Select

top

Edge

Detector

( From Prescaler )

clk

Table 16-2. Modes of Operation

Mode ICENn TCWn WGMn0

Timer/Counter Mode

of Operation TOP

Update of

OCRx at

TOV Flag

Set on

0 0 0 0 Normal 8-bit Mode 0xFF Immediate MAX (0xFF)

1 0 0 1 8-bit CTC OCRnA Immediate MAX (0xFF)

2 0 1 0 16-bit Mode 0xFFFF Immediate MAX (0xFFFF)

3 0 1 1 16-bit CTC

OCRnB,

OCRnA

Immediate MAX (0xFFFF)

410 0

8-bit Input Capture

mode

0xFF – MAX (0xFF)

511 0

16-bit Input Capture

mode

0xFFFF – MAX (0xFFFF)

1 2 ... 71 72 73 74 75 76 77 78 79 80 81 ... 167 168

Commentaires sur ces manuels

Pas de commentaire

Rainbow-electronics ATmega8HVD Manuel d'utilisateur Page 76

Commentaires sur ces manuels

Produits connexes et manuels pour Capteurs Rainbow-electronics ATmega8HVD