采用飞思卡尔MKL26Z256VLH4，硬件图如下图；现象为外部系统晶振振幅很小，软件没有检测到外部晶振。初步以为是晶振硬件问题，但是换了三个不同厂家晶振及相应电容后，问题仍然一样。
软件系统时钟初始化代码如下： 软件仿真时一直没法跳出” while((MCG->S & 0x0CU) != 0x08U) { } “ 请大神指点，谢谢！
/* SIM->SCGC5: PORTA=1 */
SIM->SCGC5 |= (uint32_t)0x0200UL; /* Enable clock gate for ports to enable pin routing */
/* SIM->CLKDIV1: OUTDIV1=1,??=0,??=0,??=0,??=0,??=0,??=0,??=0,??=0,??=0,OUTDIV4=1,??=0,??=0,??=0,??=0,??=0,??=0,??=0,??=0,??=0,??=0,??=0,??=0,??=0,??=0,??=0,??=0 */
SIM->CLKDIV1 = (uint32_t)0x10000000UL; /* Update system prescalers */
/* PORTA->PCR18: ISF=0,MUX=0 */
PORTA->PCR[18] &= (uint32_t)~0x01000700UL;
/* PORTA->PCR19: ISF=0,MUX=0 */
PORTA->PCR[19] &= (uint32_t)~0x01000700UL;
/* Switch to FBE Mode */
/* MCG_C2: LOCRE0=0,RANGE0=2,HGO0=0,EREFS0=1,LP=0,IRCS=0 */
MCG->C2 = (uint8_t)((MCG->C2 & (uint8_t)~(uint8_t)0x9BU) | (uint8_t)0x14U);
/* OSC0->CR: ERCLKEN=1,??=0,EREFSTEN=0,??=0,SC2P=1,SC4P=0,SC8P=0,SC16P=0 */
OSC0->CR = (uint8_t)0x80U;
/* MCG_C1: CLKS=2,FRDIV=3,IREFS=0,IRCLKEN=1,IREFSTEN=0 */
MCG->C1 = (uint8_t)0x9AU;
/* MCG->C4: DMX32=0,DRST_DRS=0 */
MCG->C4 &= (uint8_t)~(uint8_t)0xE0U;
/* MCG->C5: ??=0,PLLCLKEN0=0,PLLSTEN0=0,PRDIV0=1 */
MCG->C5 = (uint8_t)0x03U;
/* MCG->C6: LOLIE0=0,PLLS=0,CME0=0,VDIV0=0 */
MCG->C6 = (uint8_t)0x00U;
while((MCG->S & MCG_S_IREFST_MASK) != 0x00U) { /* Check that the source of the FLL reference clock is the external reference clock. */
}
while((MCG->S & 0x0CU) != 0x08U) { /* Wait until external reference clock is selected as MCG output */
}
/* Switch to PBE Mode */
/* MCG->C6: LOLIE0=0,PLLS=1,CME0=0,VDIV0=0 */
MCG->C6 = (uint8_t)0x40U;
while((MCG->S & 0x0CU) != 0x08U) { /* Wait until external reference clock is selected as MCG output */
}
while((MCG->S & MCG_S_LOCK0_MASK) == 0x00U) { /* Wait until locked */
}
/* Switch to PEE Mode */
/* MCG->C1: CLKS=0,FRDIV=3,IREFS=0,IRCLKEN=1,IREFSTEN=0 */
MCG->C1 = (uint8_t)0x1AU;
while((MCG->S & 0x0CU) != 0x0CU) { /* Wait until output of the PLL is selected */
}
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