[AVR] Arduino with digipot AD5293

[syntax=cpp]
#include <SPI.h>

void setup(){

  pinMode(10, OUTPUT); //CS
  pinMode(11, OUTPUT); //MOSI
  pinMode(12, INPUT);  //MISO
  pinMode(13, OUTPUT); //SCK

  Serial.begin(115200);

  writeCommand;
}

void loop(){
  unsigned int val;
  for (val = 0; val <= 1023; val++) {
    writeDigipots(val);
    //delay(10);
  }

  for (val = 1023; val > 0; val--) {
    writeDigipots(val);
    //delay(10);
  }

}


void writeDigipots(unsigned int val){
  SPI.beginTransaction(SPISettings(SPI_CLOCK_DIV8, MSBFIRST, SPI_MODE1));
  digitalWrite(10, LOW);
  //SPI.transfer(0x18); //send command byte
  //SPI.transfer(0x03);
  byte highbyte = val >> 8 + 0x04; //high wiper byte + command
  byte lowbyte = val & 0xFF;
  SPI.transfer(highbyte); //send wiper data high byte
  SPI.transfer(lowbyte); //send wiper data low byte
  digitalWrite(10, HIGH);
  SPI.endTransaction();
}

void writeCommand() {
  SPI.beginTransaction(SPISettings(SPI_CLOCK_DIV8, MSBFIRST, SPI_MODE1));
  digitalWrite(10, LOW);
  SPI.transfer(0x18); //send command high byte
  SPI.transfer(0x03); //send command low byte
  digitalWrite(10, HIGH);
  SPI.endTransaction();
}
[/syntax]