// Configure Quartz Clock CLK_DeInit(); CLK_HSECmd(ENABLE); <= 문제는 요놈 때문이었네.... CLK_SYSCLKConfig(CLK_PRESCALER_HSIDIV1); 를 아래와 같이 쓰면 문제가 없음.. CLK_DeInit(); CLK_HSIPrescalerConfig(CLK_PRESCALER_HSIDIV1); /* Clock divider to HSI/1 */ CLK_CCOConfig(CLK_OUTPUT_MASTER); /* Output Fcpu on CLK_CCO pin */