Single chip microcomputer: pcf8591 application program

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PCF8591 Applications

PCF8591 The communication interface is I2C, Then programming must comply with this protocol . Single chip microcomputer is right PCF8591 To initialize , Send a total of three bytes . First byte , and EEPROM similar , Is the device address byte , among 7 Bits represent the address ,1 Bits represent the reading and writing direction . Address high 4 The fixed position is 0b1001, The lower three are A2,A1,A0, All three of us are connected to the circuit GND, So that is 0b000, As shown in the figure .

Send to PCF8591 The second byte of will be stored in the control register , Used to control the PCF8591 The function of . Among them the first 3 Position and number 7 The bit is fixed 0, in addition 6 Each bit has its own role , As shown in the figure below , Senior students will introduce one by one .

The... Of the control byte 6 Is it DA Enable bit , This position 1 Express DA Output pin enable , Will produce analog voltage output function . The first 4 Position and number 5 Bit can realize PCF8591 Of 4 Analog inputs are configured into single ended mode and differential mode , The difference between single ended mode and differential mode , We have introduced it in previous articles , Here you only need to know that these two are configuration AD Enter the control bit of the mode .

The... Of the control byte 2 Bit is the automatic increment control bit , Automatic increment means , For example, we have 4 Channels , When we use it all , After reading the passage 0, Read it again next time , Will automatically enter the channel 1 To read , We don't need to specify the next channel , because A/D Every time I read the data , Are the results of the last conversion , So when students use the automatic increment function , Pay special attention to , What you are currently reading is the value of the previous channel . In order to maintain the universality of the program , Our code doesn't use this function , Directly made a general program .

The... Of the control byte 0 Position and number 1 Bit is the channel selection bit ,00、01、10、11 Represents the 0 To 3 Of 4 A channel selection .

Send to PCF8591 The third byte of D/A Data register , Express D/A Voltage value of analog output .D/A Let's introduce , You know the function of this byte . If we just use A/D Function words , You can not send the third byte .

Let's use a program , hold AIN0、AIN1、AIN3 The measured voltage value is displayed on the LCD , At the same time, you can turn the potentiometer , Will find AIN0 The value of has changed . /Lcd1602.c File program source code **/ （ Omit here , Refer to the code in the previous chapter ） /I2C.c File program source code **/

/*****************************main.c  File program source code ******************************/
#include <reg52.h>
bit flag300ms = 1; //300ms  Timing mark 
unsigned char T0RH = 0; //T0  High byte of overloaded value 
unsigned char T0RL = 0; //T0  The low byte of the overloaded value 

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; // General interruption 
    ConfigTimer0(10); // To configure  T0  timing  10ms
    InitLcd1602(); // Initialize the LCD 
    LcdShowStr(0, 0, "AIN0 AIN1 AIN3"); // Display channel indication 

    while (1){
    
        if (flag300ms){
    
            flag300ms = 0; // Display channel  0  The voltage of 
            val = GetADCValue(0); // obtain  ADC  passageway  0  The conversion value of 
            ValueToString(str, val); // Voltage value converted to string format 
            LcdShowStr(0, 1, str); // Display on the LCD 
            // Display channel  1  The voltage of 
            val = GetADCValue(1);
            ValueToString(str, val);
            LcdShowStr(6, 1, str);
            // Display channel  3  The voltage of 
            val = GetADCValue(3);
            ValueToString(str, val);
            LcdShowStr(12, 1, str);
        }
    }
}
/*  Read the current  ADC  Conversion value ,chn-ADC  Channel number  0~3 */
unsigned char GetADCValue(unsigned char chn){
    
    unsigned char val;
    I2CStart();
    if (!I2CWrite(0x48<<1)){
     // Addressing  PCF8591, If not answered , Stop the operation and return to  0
        I2CStop();
        return 0;
    }
    I2CWrite(0x40|chn); // Write control byte , Select the conversion channel 
    I2CStart();
    I2CWrite((0x48<<1)|0x01); // Addressing  PCF8591, Specifies the subsequent read operation 
    I2CReadACK(); // Read a byte empty first , Provide sample conversion time 
    val = I2CReadNAK(); // Read the value just converted 
    I2CStop();
    return val;
}
/* ADC  Convert the value to the string form of the actual voltage value ,str- String pointer ,val-AD  Conversion value  */
void ValueToString(unsigned char *str, unsigned char val){
    
    // Voltage value = Conversion result *2.5V/255, Type in the  25  Implied one decimal decimal 
    val = (val*25) / 255;
    str[0] = (val/10) + '0'; // Integer bit character 
    str[1] = '.'; // decimal point 
    str[2] = (val%10) + '0'; // Decimal characters 
    str[3] = 'V'; // Voltage unit 
    str[4] = '\0'; // Terminator 
}
/*  Configure and start  T0,ms-T0  Timing time  */
void ConfigTimer0(unsigned int ms){
    
    unsigned long tmp; // Temporary variable 
    tmp = 11059200 / 12; // The timer counts the frequency 
    tmp = (tmp * ms) / 1000; // Calculate the required count 
    tmp = 65536 - tmp; // Calculate timer overload value 
    tmp = tmp + 12; // Compensate for the error caused by interrupt response delay 
    T0RH = (unsigned char)(tmp>>8); // The timer overload value is split into high and low bytes 
    T0RL = (unsigned char)tmp;
    TMOD &= 0xF0; // Zero clearing  T0  Control bit of 
    TMOD |= 0x01; // To configure  T0  For mode  1
    TH0 = T0RH; // load  T0  Overload value 
    TL0 = T0RL;
    ET0 = 1; // Can make  T0  interrupt 
    TR0 = 1; // start-up  T0
}
/* T0  Interrupt service function , perform  300ms  timing  */
void InterruptTimer0() interrupt 1{
    
    static unsigned char tmr300ms = 0;
    TH0 = T0RH; // Reload overloaded values 
    TL0 = T0RL;
    tmr300ms++;
    if (tmr300ms >= 30){
     // timing  300ms
        tmr300ms = 0;
        flag300ms = 1;
    }
}

Students who read the program carefully will find , The program is in progress A/D When reading data , Two programs were used to read 2 Bytes ：I2CReadACK(); val = I2CReadNAK(); PCF8591 The conversion clock of is I2C Of SCL,8 individual SCL Cycle completes a conversion , So the current conversion result is always in the next byte 8 individual SCL Can only be read on , So the function of our first statement here is to produce a whole SCL Clock supplied to PCF8591 Conduct A/D transformation , The second time is to read the current conversion result . If we only use the second statement , Every time I read the result of the last conversion .

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