ATTINY817-MFR. datasheet(147/492 Pages) MICROCHIP

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20.3.2

Initialization

To start using the timer/counter in a basic mode, follow these steps:

•

Write a TOP value to the Period register (TCA.PER)

•

Enable the peripheral by writing a '1' to the ENABLE bit in the Control A register (TCA.CTRLA).

The counter will start counting clock ticks according to the prescaler setting in the Clock Select bit

field (CLKSEL) in TCA.CTRLA.

•

Optional: By writing a '1' to the Enable Count on Event Input bit (CNTEI) in the Event Control

•

The counter value can be read from the Counter bit field (CNT) in the Counter register (TCA.CNT).

20.3.3

Operation

20.3.3.1 Normal Operation

In normal operation, the counter is counting clock ticks in the direction selected by the Direction bit (DIR)

in the Control E register (TCA.CTRLE), until it reaches TOP or BOTTOM. The clock ticks are from the

peripheral clock CLK_PER, optionally prescaled, depending on the Clock Select bit field (CLKSEL) in the

Control A register (TCA.CTRLA).

When up-counting and TOP is reached, the counter will wrap to zero at the next clock tick. When down-

counting, the counter is reloaded with the Period register value (TCA.PER) when BOTTOM is reached.

Figure 20-4. Normal Operation

CNT written

"update"

CNT

DIR

MAX

TOP

BOTTOM

It is possible to change the Counter value in the Counter register (TCA.CNT) when the counter is running.

The write access to TCA.CNT has higher priority than count, clear, or reload, and will be immediate. The

direction of the counter can also be changed during normal operation by writing to DIR in TCA.CTRLE.

20.3.3.2 Double Buffering

The Period register value (TCA.PER) and the Compare n register values (TCA.CMPn) are all double

buffered (TCA.PERBUF and TCA.CMPnBUF).

Each buffer register has a Buffer Valid flag (PERBV, CMPnBV) in the Control F register (TCA.CTRLF),

which indicates that the buffer register contains a valid, i.e. new, value that can be copied into the

corresponding Period or Compare register. When the Period register and Compare n registers are used

for a Compare operation, the BV flag is set when data is written to the buffer register, and cleared on an

UPDATE condition. This is shown for a Compare register in below.

ATtiny417/817

Datasheet Complete

DS40001901B-page 147

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