PCINT8 datasheet(38/294 Pages) ATMEL

38 / 294 page

9219A–RFID–01/11

Atmel ATA5505 [Preliminary]

It is strongly recommended to run this sequence only once the interrupts have been disabled.

The user (code) is responsible for the correct implementation of the clock switching sequence.

Here is a “light” C-code that describes such a sequence of commands.

Warning:

In the Atmel® AVR®, only one among the three external clock sources can be enabled at a

given time. Moreover, the enables of the external clock and of the external low-frequency

oscillator are shared with the asynchronous timer.

C Code Example

void ClockSwiching (unsigned char clk

_number, unsigned char sut) {

#define CLOCK

_RECOVER

0x05

#define CLOCK

_ENABLE

0x02

#define CLOCK

_SWITCH

0x04

#define CLOCK

_DISABLE

0x01

unsigned char previous

_clk, temp;

// Disable interrupts

temp = SREG; asm ("cli");

// Save the current system clock source

CLKCSR = 1 << CLKCCE;

CLKCSR = CLOCK

_RECOVER;

_clk = CLKSELR & 0x0F;

// Enable the new clock source

CLKSELR = ((sut << 4 ) & 0x30) | (clk

_number & 0x0F);

CLKCSR = 1 << CLKCCE;

CLKCSR = CLOCK

_ENABLE;

// Wait for clock validity

while ((CLKCSR & (1 << CLKRDY)) == 0);

// Switch clock source

CLKCSR = 1 << CLKCCE;

CLKCSR = CLOCK

_SWITCH;

// Wait for effective switching

while (1){

CLKCSR = 1 << CLKCCE;

CLKCSR = CLOCK

_RECOVER;

if ((CLKSELR & 0x0F) == (clk

_number & 0x0F)) break;

}

// Shut down unneeded clock source

if (previous_clk != (clk_number & 0x0F)) {

CLKSELR = previous

_clk;

CLKCSR = 1 << CLKCCE;

CLKCSR = CLOCK

_DISABLE;

}

// Re-enable interrupts

SREG = temp;

}

PCINT8 Datasheet(PDF) 38 Page - ATMEL Corporation

PCINT8 Datasheet(HTML) 38 Page - ATMEL Corporation

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