A Arduino sketch to test the SPI library/ports

testSPI.c

// include the SPI library:
#include <SPI.h>
#include <inttypes.h>

void setup() {
  // Open serial communications and wait for port to open:
  Serial.begin(9600);
  while (!Serial) {
    ; // wait for serial port to connect. Needed for native USB port only
  }
  
  // put your setup code here, to run once:
  Serial.println("SPI.begin()...");
  SPI.begin();

}

void loop() {
  // put your main code here, to run repeatedly:
  SPI.beginTransaction( SPISettings(14000000, MSBFIRST, SPI_MODE0) );

  for( int outByte = 0 ; outByte < 10 ; outByte++ ) { 
    byte inByte = SPI.transfer( outByte);
    Serial.println("inByte=" + String( inByte ) + " outByte=" + String( outByte ) ) ;  
  }
  SPI.endTransaction();
}