Serial port sniffer

Hi, I'm writing an application that uses a serial port. I am using some kind of driver, but I'm not getting the expected results. So I would like to see what is written to and comming from the serial port. Since I use Ethereal to transparently snif the network, so I wonder if there exists something like it for the serial port. I googled and the only thing I thought usable was 'cat /dev/ttySx > data.dat &' but when I tried this the filesize was only one byte although there were sent and received many more. Is this usable for binary information ? For receive AND transmit ? Any suggestions are welcome ! Thanks. -- Met vriendelijke groeten, Koenraad Lelong R&D Manager ACE electronics n.v.