STM8 MCU - Key detection circuit design

The hardware environment uses STM8SF103, and the voltage is 3.3V. It should be noted that the IO of the STM8SF103 series can only be pulled up and suspended when used as an input port. Although it is a weak pull-up, it can still be pulled up to about 3.0V when the VCC voltage is 3.3V.

Therefore, one end of the IO port of the key detection circuit needs to be grounded instead of being pulled up externally. In the suspended mode, the IO will still have a voltage of about 0.89V, and the corresponding IO register IDR is still in a logic high state.

The software code is relatively simple, you only need to set the IO port to pull-up input. The polling code is as follows:

// Initialization only requires setting the IO port mode.

GPIO_Init (KEY2_PORT, KEY2_PIN, GPIO_MODE_IN_PU_NO_IT); //Pull-up input, no interrupt

//Key detection part

/*

#defineKEY10

#defineKEY1_PORT（GPIOD）

#defineKEY1_PIN（GPIO_PIN_4）

#defineKEY21

#defineKEY2_PORT（GPIOC）

#defineKEY2_PIN（GPIO_PIN_1）

*/

u8CheckKey（u8key）

{

if（key==KEY1）

{

if (KEY1_PORT->IDR&KEY1_PIN) //When a key is pressed, the IO port voltage will be pulled down

{

delay_5ms（）;

if (KEY1_PORT->IDR&KEY1_PIN) // low level still exists

{

while(!(KEY1_PORT->IDR&KEY1_PIN)); //Wait for release

returnKEY1;

}

}

return0;

}elseif（key==KEY2）

{

if (! (KEY2_PORT->IDR&KEY2_PIN)) //A key is detected

{

delay_5ms（）;

if (!(KEY2_PORT->IDR&KEY2_PIN)) // low level still exists

{

while (KEY2_PORT->IDR&KEY2_PIN); //Wait for release

returnKEY2;

}

}

return0;

}

return0;

}

In summary, the hardware circuit grounds one end of the key IO port. The software configuration cannot use the floating input method, as the voltage may be unstable in this way.