Problem to read and write on a serial port

From: collinm (collinm_at_laboiteaprog.com)
Date: 03/29/05 

Date: 29 Mar 2005 12:15:36 -0800

hi

i send a command to a led display, the led display is suppose to return
me some character

i write a string on a serial port

void ledDisplayExist()
{
    char msg[]={'\0', '\0', '\0', '\0', '\0', '\1', 'Z', '0', '0',
'\2', 'H', 'B', '\4' };
    int length = sizeof(msg);
    writeopen(msg, length);
    readopen();
}

int writeopen(char msg[], int size)
{
    printf("write\n");
    int fd1;
    int wr;
    fd1 = open(ledisplay, O_RDWR | O_NOCTTY | O_NDELAY );
    if (fd1 == -1)
    {
        fprintf(stderr, " %s open_port: Unable to open %s\n",
strerror(errno), ledisplay);
    }
    else
    {
        fcntl(fd1, F_SETFL, 0);

        wr=write(fd1, msg, size);
        if (wr < 0)
            fputs("write() of n bytes failed!\n", stderr);
        close(fd1);
    }
    return (fd1);
}

after i read on the serial port:

int readopen()
{
    printf("read\n");
    int fd1;
    int rd;
    char *buff=NULL;
    fd1 = open(ledisplay, O_RDONLY | O_NOCTTY | O_NDELAY );
    if (fd1 == -1)
    {
        fprintf(stderr, "%s open_port: Unable to open %s\n",
strerror(errno), ledisplay);
    }
    else
    {
        fcntl(fd1, F_SETFL, 0);
        printf(" Port 1 has been sucessfully opened and %d is the file
descriptor\n",fd1);
        rd=read(fd1, buff, 30);
        printf(" Bytes recieved are %d \n",rd);
        close(fd1);
    }
    return (fd1);
}

the string returned by the led display is suppose to be something like:
<nul><nul><nul><nul><nul><soh>"000"<stx>"G234.3432"<etx>"0237<eot>

the lenght of the returned string is under 30 character...

when i run the prog, the prog display

port série utilisé: /dev/ttyS2
connection au led display
write
read
 Port 1 has been sucessfully opened and 3 is the file descriptor

i wait a few second and nothing more is display.... i kill the program

any idea why i don't read correctly on the serial port?

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