PIC16F877 outputs sine wave signal PROTEUS simulation and program

//The PIC16F877 microcontroller outputs a sine wave signal simulation schematic diagram as follows

//20MHz crystal oscillator, outputs 500Hz sine wave, 100 points per cycle.

//1 cycle time is 2ms, the interval between two points is 2000/100=20us

//Use TMR2 to delay, 256*Tcy*K=20, Tcy=0.2, take K=1

//PR2 calculation: (PR2+1)*Tcy*1=20, PR2=99

#include

__CONFIG(0x3F3A);

#define        CS                RB1

#define        LDAC        RB2

char BUF,N;

#define  nn   100

const unsigned int SS[100]={

2048,2111,2173,2235,2297,2357,2416,2474,2530,2584,2636,2685,2733,2777,2819,2857,

2892,2924,2953,2978,2999,3017,3030,3040,3046,3048,3046,3040,3030,3017,2999,2978,

2953,2924,2892,2857,2819,2777,2733,2685,2636,2584,2530,2474,2416,2357,2297,2235,

2173,2111,2048,1985,1923,1861,1799,1739,1680,1622,1566,1512,1460,1411,1363,1319,

1277,1239,1204,1172,1143,1118,1097,1079,1066,1056,1050,1048,1050,1056,1066,1079,

1097,1118,1143,1172,1204,1239,1277,1319,1363,1411,1460,1512,1566,1622,1680,1739,

1799,1861,1923,1985};

//Macro definition, the final read of SSPBUF is a must!

#define SPI_WRITE(A)       

        SSPBUF=A;                       

        while(STAT_BF==0);       

        BUF=SSPBUF

void        main(void)

{        unsigned int x;

        TRISB=0b11111001;

        CS=1;NOP();

        LDAC=1;

        TRISC=0b00010000; //RC3 output (SCK), RC4 input (SDI), RC5 output (SDO)

        SSPEN=1; //SPI serial port enable

        CKP=1; //Idle clock is high level

        SSPM3=0;                

        SSPM2=0;

        SSPM1=0;

        SSPM0=0; //SPI master mode, clock is Fosc/4

        STAT_SMP = 1; // Sample input data at the end of the data output time

        STAT_CKE=0; //Transmit data on the rising edge of SCK

        PR2=99; //According to calculation, interrupt once every 20us

        T2CON=0b00000100;        

        N=0;

        TMR2IE=1; //Enable TMR2 interrupt

        LIKE=1;

        GIE=1;

        while(1);

}

void        interrupt INT_ISR(void)

{        unsigned        int X;

        char        i,j;

        if (TMR2IF==1)

        {        TMR2IF=0;

                X=SS[N++];

                if (N>=nn)

                        N=0;

                X+=0x7000; //HSDN=1, reference voltage buffer, amplification factor GA=1

                CS=0; //Chip select is valid

                i=X>>8;

                j=X;

                SPI_WRITE(i); //output the high 8 bits of the command

                SPI_WRITE(j); //output the lower 8 bits of the command

                LDAC=0;NOP(); //DA output is valid

                LDAC=1;NOP();

                CS=1;

        }

}