serial port comunication problem in linux

Hi all,

I am having problem comunication with serial port in linux. I have
tested the serial port with attaching a serial modem and dialing the
numbers with wvdial. it works okie but when i connect HSM to the serial

port it sends the message but i did not get a reply. mean it always
being blocked in the read function. The same hsm is working fine in
unix. so there is no problem with hsm. I am using the code as given
below for test. is there some extra configuration required. can any
body help what i m doing wrong :S

i will highly appreciate ur help.

Best Regards
Yasir Mehmood

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

        printf("Going to open HSM port:\n");

        td=fopen("test.log","a");

        fd = open("/dev/ttyS0", O_RDWR | O_NOCTTY );
        if (fd <0) {
                        fprintf(td,"Can not open the comport:\n");
                        printf("Can not open the comport:\n");
                        perror("/dev/ttyS0");
                        exit(-1);
                        }

        tcgetattr(fd,&oldtio); /* save current port settings */

        bzero(&newtio, sizeof(newtio));
        newtio.c_cflag = B9600 | CRTSCTS | CS8 | CLOCAL | CREAD;
        newtio.c_iflag = IGNPAR;
        newtio.c_oflag = 0;

        /* set input mode (non-canonical, no echo,...) */
        newtio.c_lflag = 0;

        newtio.c_cc[VTIME] = 0; /* inter-character timer unused */

        newtio.c_cc[VMIN] = 1; /* blocking read until 5 chars
received */

        tcflush(fd, TCIFLUSH);
        tcsetattr(fd,TCSANOW,&newtio);
        fprintf(td,"Going to send the Data to Hsm:\n");
        printf("Going to send the Data to Hsm:\n");
        if(write(fd,"00703C3C30",10)<=0){
                fprintf(td,"Message Can not be sent to Hsm:\n");
                printf("Message Can not be sent to Hsm:\n");
        }
        fprintf(td,"Message sent to Hsm:\n");
        printf("Message sent to Hsm:\n");

fprintf(td,"\n***********************************************:\n");
        printf("\n***********************************************:\n");

        fprintf(td,"Going to read Data from Hsm:\n");
        printf("Going to read Data from Hsm:\n");
                 res = read(fd,buf,254);
        buf[res]=0;
                fprintf(td,"Byte Read :%d\n",res);
                printf("Byte Read :%d\n",res);
                fprintf(td,"Data Read :%s\n", buf);
         printf("Data Read :%s\n", buf);
        tcsetattr(fd,TCSANOW,&oldtio);