how to make spi connection between arduino uno and dspic33ep512mc502? - arduino-uno

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.