void ValueToString(unsigned char *str, unsigned char val)
{
//电压值=转换结果*2.5V/255，式中的25隐含了一位十进制小数
val = (val*25) / 255;
str[0] = (val/10) + '0'; //整数位字符
str[1] = '.'; //小数点
str[2] = (val%10) + '0'; //小数位字符
str[3] = 'V'; //电压单位
str[4] = '\0'; //结束符
}
就val = (val*25) / 255;这句看不懂，255我理解是PCF89C51模数转换器的量程，但是乘以25是什么意思了，为何又要除以255？这里的val是从I2C读取到的电压值。
我觉得是对A/D和D/A理解太模糊导致的。
整体代码如下：
- #include <reg52.h>
- bit flag300ms = 1; //300ms定时标志
- unsigned char T0RH = 0; //T0重载值的高字节
- unsigned char T0RL = 0; //T0重载值的低字节
- 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; //开总中断
- ConfigTimer0(10); //配置T0定时10ms
- InitLcd1602(); //初始化液晶
- LcdShowStr(0, 0, "AIN0 AIN1 AIN3"); //显示通道指示
-
- while (1)
- {
- if (flag300ms)
- {
- flag300ms = 0;
- //显示通道0的电压
- val = GetADCValue(0); //获取ADC通道0的转换值
- ValueToString(str, val); //转为字符串格式的电压值
- LcdShowStr(0, 1, str); //显示到液晶上
- //显示通道1的电压
- val = GetADCValue(1);
- ValueToString(str, val);
- LcdShowStr(6, 1, str);
- //显示通道3的电压
- val = GetADCValue(3);
- ValueToString(str, val);
- LcdShowStr(12, 1, str);
- }
- }
- }
- /* 读取当前的ADC转换值，chn-ADC通道号0~3 */
- unsigned char GetADCValue(unsigned char chn)
- {
- unsigned char val;
-
- I2CStart();
- if (!I2CWrite(0x48<<1)) //寻址PCF8591，如未应答，则停止操作并返回0
- {
- I2CStop();
- return 0;
- }
- I2CWrite(0x40|chn); //写入控制字节，选择转换通道
- I2CStart();
- I2CWrite((0x48<<1)|0x01); //寻址PCF8591，指定后续为读操作
- I2CReadACK(); //先空读一个字节，提供采样转换时间
- val = I2CReadNAK(); //读取刚刚转换完的值
- I2CStop();
-
- return val;
- }
- /* ADC转换值转为实际电压值的字符串形式，str-字符串指针，val-AD转换值 */
- void ValueToString(unsigned char *str, unsigned char val)
- {
- //电压值=转换结果*2.5V/255，式中的25隐含了一位十进制小数
- val = (val*25) / 255;
- str[0] = (val/10) + '0'; //整数位字符
- str[1] = '.'; //小数点
- str[2] = (val%10) + '0'; //小数位字符
- str[3] = 'V'; //电压单位
- str[4] = '\0'; //结束符
- }
-
- void ConfigTimer0(unsigned int ms)
- {
- unsigned long tmp; //临时变量
-
- tmp = 11059200 / 12; //定时器计数频率
- tmp = (tmp * ms) / 1000; //计算所需的计数值
- tmp = 65536 - tmp; //计算定时器重载值
- tmp = tmp + 12; //补偿中断响应延时造成的误差
- T0RH = (unsigned char)(tmp>>8); //定时器重载值拆分为高低字节
- T0RL = (unsigned char)tmp;
- TMOD &= 0xF0; //清零T0的控制位
- TMOD |= 0x01; //配置T0为模式1
- TH0 = T0RH; //加载T0重载值
- TL0 = T0RL;
- ET0 = 1; //使能T0中断
- TR0 = 1; //启动T0
- }
-
- void InterruptTimer0() interrupt 1
- {
- static unsigned char tmr300ms = 0;
-
- TH0 = T0RH; //重新加载重载值
- TL0 = T0RL;
- tmr300ms++;
- if (tmr300ms >= 30) //定时300ms
- {
- tmr300ms = 0;
- flag300ms = 1;
- }
- }
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