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void ValueToString(unsigned char *str, unsigned char val)
{
//電壓值=轉(zhuǎn)換結(jié)果*2.5V/255，式中的25隱含了一位十進(jìn)制小數(shù)
val = (val*25) / 255;
str[0] = (val/10) + '0'; //整數(shù)位字符
str[1] = '.'; //小數(shù)點(diǎn)
str[2] = (val%10) + '0'; //小數(shù)位字符
str[3] = 'V'; //電壓?jiǎn)挝?br />
str[4] = '\0'; //結(jié)束符
}
就val = (val*25) / 255;這句看不懂，255我理解是PCF89C51模數(shù)轉(zhuǎn)換器的量程，但是乘以25是什么意思了，為何又要除以255？這里的val是從I2C讀取到的電壓值。
我覺得是對(duì)A/D和D/A理解太模糊導(dǎo)致的。
整體代碼如下：
- #include <reg52.h>
- bit flag300ms = 1; //300ms定時(shí)標(biāo)志
- unsigned char T0RH = 0; //T0重載值的高字節(jié)
- unsigned char T0RL = 0; //T0重載值的低字節(jié)
- void ConfigTimer0(unsigned int ms);
- unsigned char GetADCValue(unsigned char chn);
- void ValueToString(unsigned char *str, unsigned char val);
- extern void I2CStart();
- extern void I2CStop();
- extern unsigned char I2CReadACK();
- extern unsigned char I2CReadNAK();
- extern bit I2CWrite(unsigned char dat);
- extern void InitLcd1602();
- extern void LcdShowStr(unsigned char x, unsigned char y, unsigned char *str);
- void main()
- {
- unsigned char val;
- unsigned char str[10];
-
- EA = 1; //開總中斷
- ConfigTimer0(10); //配置T0定時(shí)10ms
- InitLcd1602(); //初始化液晶
- LcdShowStr(0, 0, "AIN0 AIN1 AIN3"); //顯示通道指示
-
- while (1)
- {
- if (flag300ms)
- {
- flag300ms = 0;
- //顯示通道0的電壓
- val = GetADCValue(0); //獲取ADC通道0的轉(zhuǎn)換值
- ValueToString(str, val); //轉(zhuǎn)為字符串格式的電壓值
- LcdShowStr(0, 1, str); //顯示到液晶上
- //顯示通道1的電壓
- val = GetADCValue(1);
- ValueToString(str, val);
- LcdShowStr(6, 1, str);
- //顯示通道3的電壓
- val = GetADCValue(3);
- ValueToString(str, val);
- LcdShowStr(12, 1, str);
- }
- }
- }
- /* 讀取當(dāng)前的ADC轉(zhuǎn)換值，chn-ADC通道號(hào)0~3 */
- unsigned char GetADCValue(unsigned char chn)
- {
- unsigned char val;
-
- I2CStart();
- if (!I2CWrite(0x48<<1)) //尋址PCF8591，如未應(yīng)答，則停止操作并返回0
- {
- I2CStop();
- return 0;
- }
- I2CWrite(0x40|chn); //寫入控制字節(jié)，選擇轉(zhuǎn)換通道
- I2CStart();
- I2CWrite((0x48<<1)|0x01); //尋址PCF8591，指定后續(xù)為讀操作
- I2CReadACK(); //先空讀一個(gè)字節(jié)，提供采樣轉(zhuǎn)換時(shí)間
- val = I2CReadNAK(); //讀取剛剛轉(zhuǎn)換完的值
- I2CStop();
-
- return val;
- }
- /* ADC轉(zhuǎn)換值轉(zhuǎn)為實(shí)際電壓值的字符串形式，str-字符串指針，val-AD轉(zhuǎn)換值 */
- void ValueToString(unsigned char *str, unsigned char val)
- {
- //電壓值=轉(zhuǎn)換結(jié)果*2.5V/255，式中的25隱含了一位十進(jìn)制小數(shù)
- val = (val*25) / 255;
- str[0] = (val/10) + '0'; //整數(shù)位字符
- str[1] = '.'; //小數(shù)點(diǎn)
- str[2] = (val%10) + '0'; //小數(shù)位字符
- str[3] = 'V'; //電壓?jiǎn)挝?br />
- str[4] = '\0'; //結(jié)束符
- }
-
- void ConfigTimer0(unsigned int ms)
- {
- unsigned long tmp; //臨時(shí)變量
-
- tmp = 11059200 / 12; //定時(shí)器計(jì)數(shù)頻率
- tmp = (tmp * ms) / 1000; //計(jì)算所需的計(jì)數(shù)值
- tmp = 65536 - tmp; //計(jì)算定時(shí)器重載值
- tmp = tmp + 12; //補(bǔ)償中斷響應(yīng)延時(shí)造成的誤差
- T0RH = (unsigned char)(tmp>>8); //定時(shí)器重載值拆分為高低字節(jié)
- T0RL = (unsigned char)tmp;
- TMOD &= 0xF0; //清零T0的控制位
- TMOD |= 0x01; //配置T0為模式1
- TH0 = T0RH; //加載T0重載值
- TL0 = T0RL;
- ET0 = 1; //使能T0中斷
- TR0 = 1; //啟動(dòng)T0
- }
-
- void InterruptTimer0() interrupt 1
- {
- static unsigned char tmr300ms = 0;
-
- TH0 = T0RH; //重新加載重載值
- TL0 = T0RL;
- tmr300ms++;
- if (tmr300ms >= 30) //定時(shí)300ms
- {
- tmr300ms = 0;
- flag300ms = 1;
- }
- }
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