51 MCU Programming Section 5: Keyboard Driver

1. #ifndef _KEY_H_ //Prevent repeated references to the document. If the symbol _KEY_H_ has not been defined, compile the following statement   

2. #define _KEY_H_ //As long as it is referenced once, that is, #include , the symbol _KEY_H_ is defined   

3. unsigned char keyHit( void ); //If the key is pressed, it returns non-zero, otherwise it returns 0   

4. unsigned char keyGet( void ); //Read the key value. If no key is pressed, wait until the key is pressed.   

5. void keyPut( unsigned char ucKeyVal ); //Save the key value ucKeyVal to the end of the key buffer queue   

6. void keyBack( unsigned char ucKeyVal ); //Return the key value ucKeyVal to the first key buffer queue   

7. #endif  

1. #include "key.h"   

2. #define KeyBufSize 16 //Define the number of bytes in the key buffer queue   

3. unsigned char KeyBuf[ KeyBufSize ]; //Define an unsigned character array as the key buffer queue. This queue is advanced   

4. //First-out, circular access, index from 0 to KeyBufSize-1   

5. unsigned char KeyBufWp=0; //As array subscript variable, record the storage location   

6. unsigned char KeyBufRp=0; //As array subscript variable, record the read position   

7. //If the storage position is the same as the read position, it means there is no key data in the queue   

8. unsigned char keyHit(void)   

9. { if( KeyBufWp == KeyBufRp ) return( 0 ); else return( 1 ); }   

10.     

11. unsigned char keyGet(void)   

12. { unsigned char retVal; //temporarily store the read key value   

13. while( keyHit()==0 ); //Wait for a key to be pressed, because the return value of the keyHit() function is 0, indicating no key has been pressed   

14. retVal = KeyBuf[ KeyBufRp ]; //Read the key value from the array   

15. if( ++KeyBufRp >= KeyBufSize ) KeyBufRp=0; // read position plus 1, loop back to the initial position if out of queue   

16. return( retVal );   

17. }   

18.     

19. void keyPut( unsigned char ucKeyVal )   

20. { KeyBuf[ KeyBufWp ] = ucKeyVal; //Store the key value in the array   

21. if( ++KeyBufWp >= KeyBufSize ) KeyBufWp=0; //Add 1 to the storage position, and loop back to the initial position if it exceeds the queue   

twenty two. }   

twenty three. /*********************************************** ******************************************  

24. For some reason, the read key is useless, but other tasks need to use the key, but it is inconvenient to transmit. In this case, you can return the key queue. Just like picking up the wrong letter, it is necessary to return it.  

25. ************************************************ ******************************************/  

26. void keyBack( unsigned char ucKeyVal )   

27.   

28. /*  

29. If KeyBufRp=0; minus 1, it is FFH, which is greater than KeyBufSize, that is, it returns from the head of the array to the tail of the array. Or if KeyBufRp exceeds the queue position due to interference, it must also be adjusted back to the normal position.  

30. */  

31. if( --KeyBufRp >= KeyBufSize ) KeyBufRp=KeyBufSize-1;    

32. KeyBuf[ KeyBufRp ] = ucKeyVal; //Restore key value   

33. }