ATMEGA8U2_14 Datasheet, PDF(28/310 Page) ATMEL Corporation – 125 Powerful Instructions – Most Single Clock Cycle Execution

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ATMEGA8U2_14 Datasheet, PDF (28/310 Pages) ATMEL Corporation – 125 Powerful Instructions – Most Single Clock Cycle Execution

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ATmega8U2/16U2/32U2

Figure 8-3. Example of clock switching with wake-up from Device

upstream-resume

2 Upstream Resume from device

USB

CPU Clock

non-Idle

Idle

Ext

(Suspend)

RC

non-Idle

2

Ext

External

Oscillator

RC oscillator

3ms

8.2.2 Clock switch Algorythm

Watchdog wake-up

from power-down

8.2.2.1

Swith from external clock to RC clock

if (Usb_suspend_detected())

{

Usb_ack_suspend();

Usb_freeze_clock();

Disable_pll();

Enable_RC_clock();

while (!RC_clock_ready());

Select_RC_clock();

Disable_external_clock();

}

// if (UDINT.SUSPI == 1)

// UDINT.SUSPI = 0;

// USBCON.FRZCLK = 1;

// PLLCSR.PLLE = 0;

// CLKSEL0.RCE = 1;

// while (CLKSTA.RCON != 1);

// CLKSEL0.CLKS = 0;

// CLKSEL0.EXTE = 0;

8.2.2.2

Switch from RC clock to external clock

if (Usb_wake_up_detected())

// if (UDINT.WAKEUPI == 1)

{

Usb_ack_wake_up();

// UDINT.WAKEUPI = 0;

Enable_external_clock();

// CKSEL0.EXTE = 1;

while (!External_clock_ready()); // while (CLKSTA.EXTON != 1);

Select_external_clock();

// CLKSEL0.CLKS = 1;

Enable_pll();

// PLLCSR.PLLE = 1;

Disable_RC_clock();

// CLKSEL0.RCE = 0;

while (!Pll_ready());

// while (PLLCSR.PLOCK != 1);

Usb_unfreeze_clock();

// USBCON.FRZCLK = 0;

}

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7799DâAVRâ11/10

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