將接近檢測傳感器集成到系統(tǒng)后，一個經(jīng)常遇到的問題是如何正確選擇接近檢測的門限，以便在用戶通話期間打開或關(guān)閉屏幕。門限設置須確保出現(xiàn)錯誤判斷的幾率非常低，而且能夠支持絕大多數(shù)使用者的情況。
門限滯回例程

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#define MAX44000_ADDR	0x94
#define INT_STATUS_REG	0x00
#define OFF_THRESHOLD	4600
#define OFF_DELAY		1
#define ON_THRESHOLD	4000
#define ON_DELAY		3

uint8 screenStatus;	// 0 means off, 1 means on

/*
  i2cWriteBytes()
  
  Arguments:
	uint8 address - device address
	uint8 start_reg - register where the first byte is written
	uint8 *data - data to write
	uint8 nbytes - number of bytes to write

  Consecutively writes several bytes to some i2c device starting at some 
  specified address -- implemented elsewhere
*/
void i2cWriteBytes(uint8 address,uint8 start_reg,uint8 *data,uint8 nbytes);

/*
  MAX44000InterruptHandler()

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以下代碼用于實現(xiàn)MAX44000 INT引腳的中斷處理，假設MAX44000的接近檢測傳感器設置為14位模式，并已使能中斷。此外，假設屏幕狀態(tài)初始化為1或0，詳細信息請參閱數(shù)據(jù)資料的寄存器說明部分。

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*/
void MAX44000InterruptHandler() {

	uint8 i2cData[3];
	
	i2cRead1Byte(MAX44000_ADDR,INT_STATUS_REG,&i2cData);
	if (i2cData&0x01 != 0)
		return;	// check to make sure interrupt really fired
				// this simultaneously clears the interrupt flag
	
	if (screenStatus) {
		i2cData[0] = ON_DELAY;	
		i2cData[1] = ON_THRESHOLD >> 8 & 0xBF; // set ABOVE = 0
		i2cData[2] = ON_THRESHOLD & 0xFF;
	} else {
		i2cData[0] = OFF_DELAY;	 
		i2cData[1] = OFF_THRESHOLD >> 8 | 0x40; // set ABOVE = 1
		i2cData[2] = OFF_THRESHOLD & 0xFF;
	} // set the new threshold depending on what the screen status was
	
	// set the delay and threshold after each interrupt
	i2cWriteBytes(MAX44000_ADDR,0x0A,i2cData,3);
	
	return;
} // MAX44000InterruptHandler

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