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

#define FALSE -1
#define TRUE 0

int speed_arr[] = { B38400, B19200, B9600, B4800, B2400, B1200, B300,B38400, B19200, B9600, B4800, B2400, B1200, B300, };
int name_arr[] = {38400,  19200,  9600,  4800,  2400,  1200,  300, 38400, 19200,  9600, 4800, 2400, 1200,  300, };
void set_speed(int fd, int speed){
  int   i;
  int   status;
  struct termios   Opt;
  tcgetattr(fd, &Opt);
  for ( i= 0;  i < sizeof(speed_arr) / sizeof(int);  i++) {
    if  (speed == name_arr[i]) {
      tcflush(fd, TCIOFLUSH);
      cfsetispeed(&Opt, speed_arr[i]);
      cfsetospeed(&Opt, speed_arr[i]);
      status = tcsetattr(fd, TCSANOW, &Opt);
      if  (status != 0) {
        perror("tcsetattr fd1");
        return;
      }
      tcflush(fd,TCIOFLUSH);
    }
  }
}

int set_Parity(int fd,int databits,int stopbits,int parity)
{
    struct termios options;
    if  ( tcgetattr( fd,&options)  !=  0) {
        perror("SetupSerial 1");
        return(FALSE);
    }
    options.c_cflag &= ~CSIZE;
    switch (databits)
    {
    case 7:
        options.c_cflag |= CS7;
        break;
    case 8:
        options.c_cflag |= CS8;
        break;
    default:
        fprintf(stderr,"Unsupported data size\n"); return (FALSE);
    }
    switch (parity)
    {
        case 'n':
        case 'N':
            options.c_cflag &= ~PARENB;   /* Clear parity enable */
            options.c_iflag &= ~INPCK;     /* Enable parity checking */
            break;
        case 'o':
        case 'O':
            options.c_cflag |= (PARODD | PARENB);
            options.c_iflag |= INPCK;             /* Disnable parity checking */
            break;
        case 'e':
        case 'E':
            options.c_cflag |= PARENB;     /* Enable parity */
            options.c_cflag &= ~PARODD;
            options.c_iflag |= INPCK;       /* Disnable parity checking */
            break;
        case 'S':
        case 's':  /*as no parity*/
            options.c_cflag &= ~PARENB;
            options.c_cflag &= ~CSTOPB;break;
        default:
            fprintf(stderr,"Unsupported parity\n");
            return (FALSE);
        }

    switch (stopbits)
    {
        case 1:
            options.c_cflag &= ~CSTOPB;
            break;
        case 2:
            options.c_cflag |= CSTOPB;
           break;
        default:
             fprintf(stderr,"Unsupported stop bits\n");
             return (FALSE);
    }
    /* Set input parity option */
    if (parity != 'n')
        options.c_iflag |= INPCK;
    tcflush(fd,TCIFLUSH);
    options.c_cc[VTIME] = 150;
    options.c_cc[VMIN] = 0; /* Update the options and do it NOW */

    options.c_lflag &= ~(ICANON | ECHO | ECHOE);

    if (tcsetattr(fd,TCSANOW,&options) != 0)
    {
        perror("SetupSerial 3");
        return (FALSE);
    }
    return (TRUE);
}

int main()
{
    printf("This program updates last time at %s   %s\n",__TIME__,__DATE__);
 //   printf("STDIO COM1\n");
    int fd;
    fd = open("/dev/ttyapp2",O_RDWR);
    if(fd == -1)
    {
        perror("serialport error\n");
    }
    else
    {
        printf("open ");
        printf("%s",ttyname(fd));
        printf(" succesfully\n");
    }

    set_speed(fd,9600);
    if (set_Parity(fd,8,1,'N') == FALSE)  {
        printf("Set Parity Error\n");
        exit (0);
    }
    char buf[] = "fe55aa07bc010203040506073d";
    write(fd,&buf,26);
    char buff[512];
    int nread;
    while(1)
    {

        if((nread = read(fd, buff, 512))>0)
        {
            printf("Len: %d\n",nread);
            buff[nread] = '\0';
            printf("%s\n",buff);
        }


      }
    close(fd);
    return 0;

}

serial_test.zip

Makefile

CFLAGS = -Wall -g -D_GNU_SOURCE

all: serial_test

serial_test: serial_test.o

%.o: %.c 

.PHONY: clean
clean:
	rm -f *.o serial_test