MCU Clock

Here's one of the most important discussions for uCs. The clock is a major factor that concerns me while designing a system because frequency has a direct relationship with the current.

1. Clock Sources

To generate clock, the MCU has three options :-

1. Crystall Oscillator (External to the MCU)

2. RC Oscillator (Internal)

3. PLL (Internal)

2. Configuring uC Clock using CubeMX

CubeMX provides a GUI for the developer where it can change the configuration of its CLK.

1. CO comes externally, that's why it is represented by HSE (High Speed External).

2. RC is HSI (Internal)

3. PLCLK

4. SYSCLK : It is the system clock which is used to derive all the other clocks. The SYSCLCK is derived from reference clock be it HSE, HSI or PLCLK.

• HCLK is nothing, but running clock for AHB Bus, Memory and DMA. Thus, it also drives all the peripherals such as GPIO etc which are connected AHB1.
• PCLK1 is the operating CLK for APB1 bus, that's why there's a prescalar.
• Default : RC
• Accurate : CO (It doesnt drift with temperature)
• With MCO1 (PA8) and MCO2 (PA9), you can provide SYSCLCK with Prescalar : To run another uC.
• Use logic-analyzer to check your frequency.