*** Listing 3 ***

/*
 * try to get a character from a scale; allow 1 to 2 sec.
 */
int get_response(hn_port *p)
    {
    int c;
    long int t;

    t = time(NULL) + 2;
    while (time(NULL) < t)
        if ((c = hn_pgetc(p)) != EOF)
            return c;
    return hn_pgetc(p);
    }

/*
 * write a command packet to a scale
 */
int write_command(unsigned si, unsigned fc, hn_port *p)
    {
    char buf[7];
    char *s;

    sprintf(buf, "%c%.2u%.2u%c", EOT, si, fc, ENQ);
    for (s = buf; *s != '\0'; ++s)
        if (hn_pputc(*s, p) == EOF)
            return EOF;
    if (hn_pflush(p) == EOF)
        return EOF;
    return 0;
    }