ATA6617 View Datasheet(PDF) - Atmel Corporation

Part Name

Description

MFG CO.

ATA6617

8K/16K Flash Microcontroller with LIN Transceiver, 5V Regulator and Watchdog

Atmel Corporation 

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The clock switching is performed by a sequence of commands. First, the user (code) must

make sure that the new clock source is operating. Then the ‘Clock Source Switching’ com-

mand can be issued. Once this command has been successfully completed using the

‘Recover System Clock Source’ command, the user (code) may stop the previous clock

source. 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.

C Code Example

void ClockSwiching (unsigned char clk_number, unsigned char sut) {

#define CLOCK_RECOVER

#define CLOCK_ENABLE

#define CLOCK_SWITCH

#define CLOCK_DISABLE

0x05

0x02

0x04

0x01

unsigned char previous_clk, temp;

// Disable interrupts

temp = SREG; asm ("cli");

// Save the current system clock source

CLKCSR = 1 << CLKCCE;

CLKCSR = CLOCK_RECOVER;

previous_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;

}

Warning:

In the Atmel® ATtiny87/167, 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.

58 Atmel ATA6616/ATA6617

9132D–AUTO–12/10

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