int main() {
    int fd = open( "/dev/ttyS4", O_RDWR | O_CLOEXEC | O_NOCTTY | O_NONBLOCK );
    if( fd < 0 ) {
        perror( "open" );
        return 1;
    }
    if( uart_enable_rs485( fd, true ) < 0 ) {
        perror( "uart_enable_rs485" );
        return 1;
    }
    close( fd );
    return 0;
}