DOC7707 datasheet(27/307 Pages) ETC1

27 / 307 page

7707F–AVR–11/10

AT90USB82/162

Figure 6-3.

Example of clock switching with wake-up from Device

6.2.2

Clock switch Algorythm

6.2.2.1

Swith from external clock to RC clock

if (Usb_suspend_detected())

// if (UDINT.SUSPI == 1)

{

Usb_ack_suspend();

// UDINT.SUSPI = 0;

Usb_freeze_clock();

// USBCON.FRZCLK = 1;

Disable_pll();

// PLLCSR.PLLE = 0;

Enable_RC_clock();

// CLKSEL0.RCE = 1;

while (!RC_clock_ready());

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

Select_RC_clock();

// CLKSEL0.CLKS = 0;

Disable_external_clock();

// CLKSEL0.EXTE = 0;

}

6.2.2.2

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();

// CLKSEL0.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;

}

6.2.3

Clock Selection Register 0 – CLKSEL0

USB

CPU Clock

External

Oscillator

RC oscillator

Ext

non-Idle

Idle

(Suspend)

non-Idle

upstream-resume

2 Upstream Resume from device

watchdog wake-up

from power-down

Bit

543

RCSUT1

RCSUT0

EXSUT1

EXSUT0

RCE

EXTE

CLKS

CLKSEL0

Read/Write

R/W

Initial Value

See Bit Description

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