如何使用微控制器检测键盘矩阵中开关的释放？

Question

我想要检测按键矩阵中开关的释放。考虑一个4*4键矩阵，微控制器的扫描可以很容易地完成，以检测按键。但是，我想在发生释放时也检测到它们。有没有更有效的方法来做到这一点，而不是仅仅对未按下的每个状态更改中断进行另一次扫描？

Answer 1

矩阵键盘扫描不需要任何中断。您应该创建定期调用的扫描函数。最好的方法是将每个键作为位存储在某个变量中-您有4x4键盘，所以uint16_t将完美地适合您。XOR运算符非常适合检测按键变化。另外，不要忘记实现一些关键的去抖动功能。

我建议使用下面的“伪”代码或类似的代码(我希望其中没有bug )：

#define ROW_COUNT         4
#define COL_COUNT         4
#define DEBOUNCE_TIMEOUT  10   // In milliseconds

typedef uint16_t KeyState;

// This function returns current keyboard state and
// fills upKeys with keys that were pressed and downKeys with keys that were released
// It expects that key down is logic H, up is logic L
KeyState KeyboardState(KeyState* upKeys, KeyState* downKeys)
{
  static KeyState lastState = 0;
  static KeyState lastValidState = 0;
  static Timestamp lastTimestamp = 0;
  KeyState currentState = 0;
  uint8_t x, y;

  // Set defaults
  if (upKeys)
    *upKeys = 0;
  if (downKeys)
    *downKeys = 0;

  for(y = 0; y < ROW_COUNT; y++)
  {
    // Set appropriate row pin to H
    SetRowPinH(y);
    // Just to be sure that any parasitic capacitance gets charged
    SleepMicro(10);
    for(x = 0; x < COL_COUNT; x++)
    {
      // Check key pressed
      if (IsColPinSet(x))
        currentState |= 1 << ((y * COL_COUNT) + x);
    }
    // And don't forget to set row pin back to L
    SetRowPinL(y);
  }

  // Now lets do debouncing - this is important for good functionality
  // Matrix state should not change for some time to accept result
  if (lastState == currentState)
  {
    // Check if time has passed
    if ((TimestampNowMilli() - lastTimestampMilli) >= DEBOUNCE_TIMEOUT)
    {
      // Let's detect up/down changes first - it's easy, just use XOR for change detection
      if (upKeys)
        *upKeys = currentState & (lastValidState ^ currentState);
      if (downKeys)
        *downKeys = (~currentState) & (lastValidState ^ currentState);
      lastValidState = currentState;
    }
  }
  else
  {
    // Current state differs from previous - reset timer
    lastTimestampMilli = TimestampNowMilli();
  }
  lastState = currentState;

  return lastValidState;
}

int main()
{
  KeyState upKeys;
  KeyState downKeys;
  KeyState currentKeys;
  while(1)
  {
    currentKeys = KeyboardState(&upKeys, &downKeys);
    if (upKeys & 0x0001)
      printf("Key 1 pressed\n");
    if (downKeys & 0x0001)
      printf("Key 1 released\n");
  }
}