STM8S study notes-clock control 1

1. As shown in Figure 13, the STM8S microcontroller has four main clock sources to choose from:

1).1-24MHz external crystal oscillator (HSE).

2).Maximum 24MHz external clock (HSE ext).

3).16MHz high speed internal RC oscillator (HSI).

4).128KHz low speed internal RC oscillator (LSI).

2. The main clock can be switched from any of these four clock sources, and the switching process can be automatic switching or manual switching.

Automatic switching process: enable the corresponding clock source, enable switching, and wait for the switching to complete.

For example: Switching from HSI to external HSE, the subroutine is as follows:

void CLKToHSE(void)

{

    while(!(CLK_ECKR&0x02)); //Wait for HSE to be ready

    CLK_ECKR |= 0x01; // Enable HSE

    CLK_SWCR |= 0x20; //Enable switching

    CLK_SWR = 0xB4; // (0xE1----HSI )

                               // (0xD2 ----LSI)

                             //(0xB4----HSE)

    while(!(CLK_SWCR&0x01)); //Wait for clock switching to complete

    CLK_ICKR &= ~0x01; //Disable HSI

}

Manual switch:

Manual switching is similar to automatic switching, except that you have to wait until the clock is stable before switching.

For example, the HSI switches to the internal LSI, and the subroutine is as follows:

void CLKToLSI(void)

{

    while(!(CLK_ICKR&0x10)); //Wait for LSI to be ready

    CLK_ICKR |= 0x08; // Enable LSI

     CLK_SWR = 0xD2; // (0xE1----HSI)

                                // (0xD2 ----LSI)

                               // (0xB4----HSE)

     while(!(CLK_SWCR&0x08));

    CLK_SWCR |= 0x20; //Enable switching

    CLK_ICKR &= ~0x01; //Disable HSI

}

3. Clock division

HSI can be divided by HSIDIV[1:0] of CLK_CKDIVR. The division factor can be 1, 2, 4, or 8.

The CPU clock can be divided by CPUDIV[2:0] of CLK_CKDIVR. The division ratio can be 1, 2, 4, 8, 16, 32, 64, 128.

The peripheral clock can be enabled or disabled through CLK_PCKENR1 and CLK_PCKENR2. Under reset, all peripheral clocks are enabled by default. If you are not familiar with it, you can choose the default to prevent the peripherals from being used without configuring the clock. Disabling unnecessary peripherals can reduce system power consumption.

There are also clock security system CSS, clock output, clock interrupt, SWIM clock control, HSI clock calibration, etc. We will discuss them next time.