Linux Serial port programming

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <termios.h>
#include <stdio.h>
#include <strings.h>
#include <stdlib.h>
#include <unistd.h>

#define BAUDRATE B9600
#define MODEMDEVICE "/dev/ttyS0"
#define _POXSIX_SOURCE 1
#define FALSE 0
#define TRUE 1

volatile int STOP=FALSE;

int main()
{
 int fd, c, res;
 struct termios oldtio, newtio;
 char buf[255];

 //fd = open(MODEMDEVICE, O_RDWR | O_NOCTTY | O_NDELAY);
 //fd = open(MODEMDEVICE, O_RDWR | O_NDELAY);
 fd = open(MODEMDEVICE, O_RDWR );
 if(fd < 0){
  perror("Cannot open device");
  exit(-1);
 }

 tcgetattr(fd, &oldtio); 

 bzero(&newtio, sizeof(newtio));

 newtio.c_cflag = BAUDRATE | CRTSCTS | CS8 | CLOCAL | CREAD;
 newtio.c_iflag = IGNPAR;
 newtio.c_oflag = 0;

 newtio.c_lflag = 0;

 newtio.c_cc[VTIME] = 0;
 newtio.c_cc[VMIN] = 5;

 tcflush(fd, TCIFLUSH);
 tcsetattr(fd, TCSANOW, &newtio);

 while(STOP == FALSE){
  res = read(fd, buf, 255);
  buf[res] = '\0';
  printf("%s -> %d\n", buf, res);
  if(buf[0] == 'z') STOP=TRUE;
 }
 tcsetattr(fd, TCSANOW, &oldtio);

 return 0;
}