FAQ
- M051 Base Series(95)
- M0518 Series(97)
- M0519 Series(43)
- M0564 Series(1)
- Mini51 Base Series(90)
- Nano100/102 Base Series(101)
- Nano103 Base Series(10)
- Nano110/112 LCD Series(100)
- Nano120 USB Series(111)
- Nano130 Advanced Series(110)
- NUC029 Series(94)
- NUC100/200 Advanced Series(102)
- NUC120/122/123/220 USB Series(116)
- NUC121/125 Series(1)
- NUC126 USB Series(2)
- NUC130/230 CAN Series(103)
- NUC131/NUC1311 CAN Series(98)
- NUC140/240 Connectivity Series(114)
- M451 Base Series(118)
- M451M Series(117)
- M452 USB Series(130)
- M4521 USB Series(1)
- M453 CAN Series(128)
- M463 CAN FD/USB HS Series(1)
- M467 Ethernet/Crypto Series(1)
- M471 Series(1)
- M479 Motor Control Series(1)
- M481 Base Series(4)
- M482 USB FS OTG Series(4)
- M483 CAN Series(4)
- M484 USB HS OTG Series(4)
- M485 Crypto Series(4)
- M487 Ethernet Series(4)
- M4TK Touch Key Series(25)
- NUC442/472 Series(130)
- NUC472 Series(1)
- NUC505 Series(138)
FAQ
Why can’t the clock source of HCLK be switched to PLL when the system clock source is initialized with the following commands? CLK->CLKSEL0 = (CLK->CLKSEL0 & ~CLK_CLKSEL0_HCLKSEL_Msk); CLK->CLKSEL0 |= CLK_CLKSEL0_HCLKSEL_PLL; Issue Date：2016-11-29
Q: Why can’t the clock source of HCLK be switched to PLL when the system clock source is initialized with the following commands?
CLK->CLKSEL0 = (CLK->CLKSEL0 & ~CLK_CLKSEL0_HCLKSEL_Msk);
CLK->CLKSEL0 |= CLK_CLKSEL0_HCLKSEL_PLL;
A: In the execution of the first command line,
CLK->CLKSEL0 = (CLK->CLKSEL0 & ~CLK_CLKSEL0_HCLKSEL_Msk);
HCLKSEL (CLKSEL0 [2: 0]) is set to 0x00. When HCLKSEL is set to 0x00, as shown below, the clock source of HCLK is switched to external crystal.
If the external crystal is not stable or enabled at this time, the switching clock source will fail and the HCLKSEL will be remain its default setting (initialized as 0x07, clock source as HIRC).
Therefore, in the execution of the second command line,
CLK->CLKSEL0 |= CLK_CLKSEL0_HCLKSEL_PLL;
HCLKSEL cannot be correctly set to PLL and HCLK cannot be switched to PLL.
To switch the clock source, user needs to make sure that the clock source to be switched is stable. It is recommended to switch the clock source using the following methods:
1. Write a value directly
CLK->CLKSEL0 = (CLK->CLKSEL0 & ~CLK_CLKSEL0_HCLKSEL_Msk) | CLK_CLKSEL0_HCLKSEL_PLL;
2. Call function
CLK_SetHCLK(CLK_CLKSEL0_HCLKSEL_PLL, CLK_CLKDIV_HCLK(2));
| Products: | Microcontrollers ,8bit 8051 MCUs ,Low Pin Count 8051 Series ,Standard 8051 Series ,Arm Cortex-M0 MCUs ,M051 Base Series ,M0518 Series ,M0519 Series ,Mini51 Base Series ,Nano100/102 Base Series ,Nano103 Base Series ,Nano110/112 LCD Series ,Nano120 USB Series ,Nano130 Advanced Series ,NUC029 Series ,NUC100/200 Advanced Series ,NUC120/122/123/220 USB Series ,NUC130/230 CAN Series ,NUC131/NUC1311 CAN Series ,NUC140/240 Connectivity Series ,Arm Cortex-M4 MCUs ,M451 Base Series ,M451M Series ,M452 USB Series ,M453 CAN Series ,M4TK Touch Key Series ,NUC442/472 Series ,NUC505 Series |
|---|---|
| Applications: | |
| Function: | Peripherals,ARM,Cortex-M0,Cortex-M4,Clock Control,HIRC,HXT,PLL |