按键检测

适用于如下电路的按键检测，定时调用ReadKey()函数查询按键状态，将返回按键动作中KEY_UP、KEY_PRESSED、KEY_DOWN、KEY_REPEATED、KEY_RELEASED五种状态。要检测多个按键时，需要为每个按键分配一个tagKEYSTATE结构，tagKEYSTATE中的nRepeatDelay属性可以设置按键自动重复功能和重复速率。

左右两个电路作用一样，区别是左边CPU的输入端常态为高电位，按下按键时为低电位；右边的常态为低电位，按下按键是高电位。对于按下为低电位的按键电路，应该把I/O端口的值取反后再调用ReadKey()函数。

Keys.h代码

#define KEY_UP		0
#define KEY_PRESSED	1
#define KEY_DOWN	2
#define KEY_RELEASED	3
#define KEY_REPEATED	4

typedef struct tagKEYSTATE
{
	unsigned char nPinState;
	unsigned char nPinStateBuff;
	unsigned char nCounter;
	unsigned char nRepeatDelay;
} KEYSTATE;

unsigned char ReadKey(unsigned char nPinState, KEYSTATE * KeyState);

Keys.c代码

#include "Keys.h"

unsigned char ReadKey(unsigned char nPinState, KEYSTATE * KeyState)
{
	unsigned char ks = KEY_UP;

	if (KeyState->nPinState == nPinState)
	{
		if (KeyState->nPinStateBuff == KeyState->nPinState)
		{
			if (KeyState->nPinStateBuff == 1)
			{
				if (KeyState->nRepeatDelay != 0)
				{
					if (KeyState->nCounter == 0)
					{
						KeyState->nCounter = KeyState->nRepeatDelay;
						ks = KEY_REPEATED;
					}
					else
					{
						KeyState->nCounter --;
						ks = KEY_DOWN;
					}
				}
			}
		}
		else
		{
			KeyState->nPinStateBuff = KeyState->nPinState;

			if (KeyState->nPinStateBuff == 1)
			{
				KeyState->nCounter = KeyState->nRepeatDelay;
				ks = KEY_PRESSED;
			}
			else
				ks = KEY_RELEASED;
		}
	}
	else
	{
		if (KeyState->nPinState == 0)
			ks = KEY_UP;
		else
			ks = KEY_DOWN;

		KeyState->nPinState = nPinState;
	}

	return ks;
}