MCU key scanning program state machine method

#define key_input PIND.7 // Key input port
#define key_state_0 0
#define key_state_1 1
#define key_state_2 2

char read_key(void)
{
                static char key_state = 0;
                char key_press, key_return = 0;

                key_press = key_input; // Read key I/O level
                switch (key_state)
                {
                        case key_state_0: // Key initial state
                                if (!key_press) key_state = key_state_1; // Key is pressed, state changes to key confirmation state
                                break;
                        case key_state_1: // Key confirmation state
                                if (!key_press)
                                {
                                        key_return = 1; // Key is still pressed, key confirmation output is "1"
                                        key_state = key_state_2; // State changes to key release state
                                }
                                else
                                        key_state = key_state_0; // Key is released, change to key initial state
                                break;
                        case key_state_2:
                                if (key_press) key_state = key_state_0; // Key is released, change to key initial state
                                break;
                }       
            return key_return;
}

Another principle is that the execution time of the designed interrupt service function should be as short as possible. In this way, if multiple interrupts are used in the system, even if the interrupt nesting method is not adopted, it can ensure that the system can respond to the requests of each interrupt in time.

Therefore, I like to use only one flag variable in the timer interrupt, so that the interrupt service function has the fastest execution time and will not block the timely response of other interrupts. In the main program, the flag variable is judged and then the key is scanned. Although the scanning interval is not strictly 10ms at this time, there are more or less delays, and the delay is uncertain, but it will not affect the correctness of the key scanning (the process of one key is at least 300ms).

Set a timer interrupt to scan the key every 10MS. , read the value. . If there are multiple keys and extra timers, you can try this method, which is efficient. It is just right for STM32. cool.