Code:
serialport.Write(100)
this should send string, so i guess you'll need to change the SERIN to
Code:
serin porta.1,t2400,#pcsig
I'll second Ardhuru's advice. A serial COMport sniffer is always handy to have on hand. I use HHDSoft's one
http://www.hhdsoftware.com

There's a load of those here and there, some are 100% free.

Having one on hand... priceless!