open ,write, read close 관련 질문있습니다.

int		nComDev;
long 	BAUD;
long 	DATABITS;
long 	STOPBITS;
long 	PARITYON;
long 	PARITY;
struct termios oldtio, newtio;
 
	nComDev = open ("/dev/ttyUSB4", O_RDWR | O_NONBLOCK | O_NOCTTY);
 
	if (nComDev < 0)
	{
		// FILE Open Fail
		 printf( "Device OPEN FAIL %s\n", "/dev/ttyUSB4" );
		 return -1;
	}
 
		tcgetattr(nComDev,&oldtio); // save current port settings
 
		// set new port settings for canonical input processing
		BAUD=B115200;
		DATABITS = CS8;
		STOPBITS= 0;
		PARITY = 0;
		PARITYON=0;
 
		newtio.c_cflag = BAUD | CRTSCTS | DATABITS | STOPBITS | PARITYON | PARITY | CLOCAL | CREAD;
		newtio.c_iflag = IGNPAR;
		newtio.c_oflag = 0;
		newtio.c_lflag = 0;       //ICANON;
		newtio.c_cc[VMIN]=1;
		newtio.c_cc[VTIME]=0;
		tcflush(nComDev, TCIFLUSH);
		tcsetattr(nComDev,TCSANOW,&newtio);
 
		res = write((LPSTR)"AT",strlen("AT"));
 
		while( (read_n = read(nComDev, InData, sizeof(InData))) > 0)
		{
 
			printf("\nREADING....\n");
 
			for(i=0;i<read_n;i++)
			{
				printf("%c",InData[i]);
			}
 
			memset(InData,0x00,sizeof(InData));
		}
 
	close(nComDev);