how to make spi connection between arduino uno and dspic33ep512mc502?

Question

• i just want to test spi comunication between arduino uno and dspic33ep512mc502, i use serial port to see receiving data from microcontroller; -arduino uno is master -dspic33ep512mc502 is slave

here is my code for Arduino Uno :

#include<SPI.h>

byte y=1;
void setup() {

Serial.begin(9600);
SPI.begin(); 
SPI.setDataMode(SPI_MODE1);     
 digitalWrite(SS,HIGH);
// SPI.setBitOrder( LSBFIRST);
 SPI.setBitOrder( MSBFIRST);
}

int trnasfer_spi(int d)
{
digitalWrite(SS,LOW);  
byte r=SPI.transfer(7); 
digitalWrite(SS,HIGH);
return r; 
}

void loop() {

 if (Serial.available() > 0) {
     // read the incoming byte:
        int incomingByte = Serial.read();
        y=trnasfer_spi(incomingByte);
         }       

Serial.print(y, DEC);
delay(1000);


}

here is dspic33ep512mc502 code(just for spic comunication):

initialization :

ANSELBbits.ANSB0 = 0; 
TRISBbits.TRISB0 = 1;  
TRISBbits.TRISB7 = 1;  
TRISBbits.TRISB8 = 0;  
TRISBbits.TRISB9 = 1;  
SPI1CON1bits.DISSCK = 0;
SPI1CON1bits.DISSDO = 0; 
SPI1CON1bits.MODE16 = 0; 
SPI1CON1bits.SMP = 0;    
SPI1CON1bits.CKP = 0;    
SPI1CON1bits.CKE = 1;    
SPI1CON1bits.MSTEN = 0;  
SPI1CON1bits.SSEN = 1;   

//Setari registru SPI1STAT
SPI1STATbits.SPIROV = 0; 
SPI1STATbits.SPIEN  = 1; 

IFS0bits.SPI1IF = 0; 
IEC0bits.SPI1IE = 1; 
IPC2bits.SPI1IP = 6; 
SPI1BUF =3; 

SPI1Interrupt:

 void __attribute__((__interrupt__)) _SPI1Interrupt(void)
 {

    IFS0bits.SPI1IF = 0;           
    SPI1STATbits.SPIROV = 0;       
    SPI1BUF=3;


    };

i expect to see value 3 on serial monitor, but i see only value 7 or 255.

Answer 1

SPI reads and writes at the same time, so a write to the register must be followed by a read, otherwise the next read won't work.

So try to read spi1buf after writing it.