Hi

"I registered the Control.dll using Regsvr32 and it succeeded."

then it's a COM dll (VB can't produce straight C like dll's as long as i know)

load it into the Object browser (Menu->Tools->Object browser)
and explore it's objects & their methods

you have to use:

loObj = CREATEOBJECT('yourVBDll.NameOfClass')
loObj.OpenPort() ..


Regards
Christian