ATmega16U4 datasheet(112/408 Pages) ATMEL

112 / 408 page

112

7766D–AVR–01/09

ATmega16U4/ATmega32U4

Note:

1. See “Code Examples” on page 8.

The assembly code example requires that the r17:r16 register pair contains the value to be writ-

ten to TCNTn.

14.2.1

Reusing the Temporary High Byte Register

If writing to more than one 16-bit register where the high byte is the same for all registers written,

then the high byte only needs to be written once. However, note that the same rule of atomic

operation described previously also applies in this case.

14.3

Timer/Counter Clock Sources

The Timer/Counter can be clocked by an internal or an external clock source. The clock source

is selected by the Clock Select logic which is controlled by the Clock Select (CSn2:0) bits

located in the Timer/Counter control Register B (TCCRnB). For details on clock sources and

prescaler, see “Timer/Counter0, Timer/Counter1, and Timer/Counter3 Prescalers” on page 88.

14.4

Counter Unit

The main part of the 16-bit Timer/Counter is the programmable 16-bit bi-directional counter unit.

Figure 14-2 shows a block diagram of the counter and its surroundings.

TIM16_WriteTCNTn:

; Save global interrupt flag

r18,SREG

; Disable interrupts

cli

; Set TCNTn to r17:r16

out

TCNTnH,r17

out

TCNTnL,r16

; Restore global interrupt flag

out

SREG,r18

ret

C Code Example(1)

void

TIM16_WriteTCNTn( unsigned int i )

{

unsigned char

sreg;

unsigned int

/* Save global interrupt flag */

sreg = SREG;

/* Disable interrupts */

__disable_interrupt();

/* Set TCNTn to i */

TCNTn = i;

/* Restore global interrupt flag */

SREG = sreg;

}

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