Микроконтроллеры

//----------------------------------------------------------------
// Oscillator Configuration
//----------------------------------------------------------------

    SFRPAGE = 0x00;
    FLSCL = 0x80;   // FLASH Memory Control
    SFRPAGE = 0x0F;
    OSCXCN = 0x67;	// EXTERNAL Oscillator Control Register	
    for (n = 0; n < 383; n++) ;            // wait for osc to start
    while ( (OSCXCN & 0x80) == 0 );        // wait for xtal to stabilize
    PLL0DIV = 0x01; // PLL pre-divide Register 
    PLL0MUL = 5; // PLL Clock scaler Register
    PLL0FLT = 0x0F; // PLL Filter Register
    PLL0CN = 0x05;  // PLL Control Register
    for(b = 0; b < 15; b++);               // wait at least 5us
    PLL0CN |= 0x02;                        // enable PLL
    while ( (PLL0CN & 0x10) == 0 );        // wait for PLL to lock



    CLKSEL = 0x01;  // Oscillator Clock Selector
	OSCICN = 0x00;	// Internal Oscillator Control Register

Как только доходит до переключения мультиплексора (CLKSEL = 0x01) - зависает.