SCM signal generator program

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MCU signal generator program

With D/A This weapon , We can not only output square wave signals , You can output any waveform , Like sine wave 、 Triangle wave 、 Sawtooth wave, etc . Take sine wave as an example , First we need to build a sine wave table . These do not need to be calculated one by one , The sine wave data table can be found by searching , Then we can choose a certain amount of data as the sine wave meter of our program according to the time parameters , Our program code selects 32 A little bit .

#include <reg52.h>

unsigned char code SinWave[] = {
     // Sine wave meter 
    127, 152, 176, 198, 217, 233, 245, 252,
    255, 252, 245, 233, 217, 198, 176, 152,
    127, 102, 78, 56, 37, 21, 9, 2,
    0, 2, 9, 21, 37, 56, 78, 102
};
unsigned char code TriWave[] = {
     // Triangular wave table 
    0, 16, 32, 48, 64, 80, 96, 112,
    128, 144, 160, 176, 192, 208, 224, 240,
    255, 240, 224, 208, 192, 176, 160, 144,
    128, 112, 96, 80, 64, 48, 32, 16
};
unsigned char code SawWave[] = {
     // Sawtooth wave meter 
    0, 8, 16, 24, 32, 40, 48, 56,
    64, 72, 80, 88, 96, 104, 112, 120,
    128, 136, 144, 152, 160, 168, 176, 184,
    192, 200, 208, 216, 224, 232, 240, 248
};
unsigned char code *pWave; // Wave meter pointer 
unsigned char T0RH = 0; //T0  High byte of overloaded value 
unsigned char T0RL = 0; //T0  The low byte of the overloaded value 
unsigned char T1RH = 1; //T1  High byte of overloaded value 
unsigned char T1RL = 1; //T1  The low byte of the overloaded value 

void ConfigTimer0(unsigned int ms);
void SetWaveFreq(unsigned char freq);
extern void KeyScan();
extern void KeyDriver();
extern void I2CStart();
extern void I2CStop();
extern bit I2CWrite(unsigned char dat);

void main(){
    
    EA = 1; // General interruption 
    ConfigTimer0(1); // To configure  T0  timing  1ms
    pWave = SinWave; // Default sine wave 
    SetWaveFreq(10); // Default frequency  10Hz

    while (1){
    
        KeyDriver(); // Call the key driver 
    }
}
/*  Key action function , Perform the corresponding operation according to the key code ,keycode- Key code  */
void KeyAction(unsigned char keycode){
    
    static unsigned char i = 0;
    if (keycode == 0x26){
     // Up key , Switching waveforms 
        // stay  3  Cyclic switching between waveforms 
        if (i == 0){
    
            i = 1;
            pWave = TriWave;
        }else if (i == 1){
    
            i = 2;
            pWave = SawWave;
        }else{
    
            i = 0;
            pWave = SinWave;
        }
    }
}

/*  Set up  DAC  Output value ,val- The set value  */
void SetDACOut(unsigned char val){
    
    I2CStart();
    if (!I2CWrite(0x48<<1)){
     // Addressing  PCF8591, If not answered , Stop the operation and return to 
        I2CStop();
        return;
    }
    I2CWrite(0x40); // Write control byte 
    I2CWrite(val); // write in  DA  value 
    I2CStop();
}
/*  Set the frequency of the output waveform ,freq- Set the frequency  */
void SetWaveFreq(unsigned char freq){
    
    unsigned long tmp;
    tmp = (11059200/12) / (freq*32); // The timer counts the frequency , Is the waveform frequency  32  times 
    tmp = 65536 - tmp; // Calculate timer overload value 
    tmp = tmp + 33; // Correct the error caused by interrupt response delay 
    T1RH = (unsigned char)(tmp>>8); // The timer overload value is split into high and low bytes 
    T1RL = (unsigned char)tmp;
    TMOD &= 0x0F; // Zero clearing  T1  Control bit of 
    TMOD |= 0x10; // To configure  T1  For mode  1
    TH1 = T1RH; // load  T1  Overload value 
    TL1 = T1RL;
    ET1 = 1; // Can make  T1  interrupt 
    PT1 = 1; // Set to high priority 
    TR1 = 1; // start-up  T1
}
/*  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 + 28;// 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 key scan  */
void InterruptTimer0() interrupt 1{
    
    TH0 = T0RH; // Reload overloaded values 
    TL0 = T0RL;
    KeyScan(); // Key scan 
}
/* T1  Interrupt service function , Execute waveform output  */
void InterruptTimer1() interrupt 3{
    
    static unsigned char i = 0;
    TH1 = T1RH; // Reload overloaded values 
    TL1 = T1RL;
    // Circularly output the data in the wave table 
    SetDACOut(pWave[i]);
    i++;
    if (i >= 32){
    
        i = 0;
    }
}   

This program can be passed through “ Up ” Press the key to switch the waveform output , The timing refresh of waveform output is controlled by timer T1 Time to complete , change T1 The timing period can change the output frequency of the waveform .D/A The output cannot be connected to the display interface , So we use an oscilloscope to grab the waveform and show it to you

These figures can visually see the waveform output by our program . Careful students will find that there are many small serrations on our waveform , There is no smooth connection . It's because of us DA At most, it can only output 0～Vref Between 256 Discrete voltage values , Instead of continuous arbitrary values , So each discrete value will last for a certain time , Then jump to the next discrete value , So it shows the sawtooth on the waveform . In actual development , All we need to do is DA The next stage plus a low-pass filter circuit , You can make the sawtooth waveform smooth .

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