Begginer Question about TK::filevent

[dhillon2004]

Hello All,
I am beginer in Perl. I am trying a serial port data logging
application.
Requirement of my application is that it should be capable of
receiving and transmitting on same or diffrent ports depending on the
options.
I transmit 34 Bytes of data and would receive 34 bytes of data in
return. Now the problem is that I have to time stamp the packet on the
receive side whenever comlete pkt is received.
I am on windows XP machine and I have Active State Perl 5.8
I am using win32::serialPort pm for configuration setup.
I am trying to use Tk::filevent to iniatiate a call back whenever my
Serial port becomes readable.
But i am getting an error "Not a Glob reference in IO pm"
I have given the follwoing command:

$mw->fileevent($ob, 'readable', \&read_comport);
$mw is an my mainwindow instance
$ob is the object of my comport.
I wish to call &read_comport whenever my comport becomes readable
But i get the above error as mentioned above and my program quits.

I am doing right.
Can the object $ob be passed as fileHandle to fileevent??
or I am interprating something wrong!!
Your help would behighly apprecaited!!
Thanks a lot in advance!!

Sincerely,
Mandeep