# open serial port, create instance of Win32::RS232Port object
$self->{serport} =  Win32::RS232Port->new($comport_name, handshake => 'rts', baudrate => 9600);
if (!defined $self->{serport}) { die "Could not open reference COM port"; }

# manually set state of handshaking output lines:
$self->{serport}->rts_active(1);
$self->{serport}->dtr_active(1);

# transmit some data:
$self->{serport}->qtx("SYST:ERR?\r\n");

sub poll {
    # call this function regularly to check for received data and to pass on any queued data for transmission
    my $self = shift;
    
    if ( defined $self->{serport} ) {
        # pass on any queued data for transmission
        $self->{serport}->poll_tx;
        
        # handle incoming data: here I'm just appending it to $self->{com_rxd} where it can be picked up by code that's interested.
        my $rx = $self->{serport}->rx_data;
        if ($rx ne q{}) {
            $self->{com_rxd} = q{} if !defined $self->{com_rxd};
            $self->{com_rxd} .= $rx;
        }
    }
}

sub wait_for_tx_done {
    my $self = shift;
    my $tstart = time;
    while (defined $self->{serport} && $self->{serport}->tx_pending) {
        $self->poll();
        die "Timeout on serial port transmission\n" if time > $tstart + 10;
    }
}

# close the serial port
$self->{serport}->close();