51单片机4x4按键Void

#include <REGX52.H>

char key_16(){
	unsigned char KeyNumber = 0;
	
	/*第一列*/
	P1 = 0xF7;
	switch(P1){
		case 0x77:
			while(P1 == 0x77);
			KeyNumber = 1;
		break;
		case 0xB7:
			while(P1 == 0xB7);
			KeyNumber = 5;
		break;
		case 0xD7:
			while(P1 == 0xD7);
			KeyNumber = 9;
		break;
		case 0xE7:
			while(P1 == 0xE7);
			KeyNumber = 13;
		break;
	}

	/*第二列*/
	P1 = 0xFB;
	switch(P1){
		case 0x7B:
			while(P1 == 0x7B);
			KeyNumber = 2;
		break;
		case 0xBB:
			while(P1 == 0xBB);
			KeyNumber = 6;
		break;
		case 0xDB:
			while(P1 == 0xDB);
			KeyNumber = 10;
		break;
		case 0xEB:
			while(P1 == 0xEB);
			KeyNumber = 14;
		break;
	}

	/*第三列*/
	P1 = 0xFD;
	switch(P1){
		case 0x7D:
			while(P1 == 0x7D);
			KeyNumber = 3;
		break;
		case 0xBD:
			while(P1 == 0xBD);
			KeyNumber = 7;
		break;
		case 0xDD:
			while(P1 == 0xDD);
			KeyNumber = 11;
		break;
		case 0xED:
			while(P1 == 0xED);
			KeyNumber = 15;
		break;
	}

	/*第四列*/
	P1 = 0xFE;
	switch(P1){
		case 0x7E:
			while(P1 == 0x7E);
			KeyNumber = 4;
		break;
		case 0xBE:
			while(P1 == 0xBE);
			KeyNumber = 8;
		break;
		case 0xDE:
			while(P1 == 0xDE);
			KeyNumber = 12;
		break;
		case 0xEE:
			while(P1 == 0xEE);
			KeyNumber = 16;
		break;
	}
	
	return KeyNumber;
}