I'm sorry - wrong code :-(
That should be ocommform.comminput.input to read the port. Here is the basic definition that uses a form class property "inbuffer" to hold the data. It could just as easily be a property of your control subclass.
DEFINE CLASS incomm AS CUSTOM
IMPLEMENTS dmscommevents IN mscomm32.ocx
PROCEDURE dmscommevents_oncomm
WITH ocommform
IF .comminput.commevent = 2
.inbuffer = .inbuffer + .comminput.INPUT
ENDWITH
ENDPROC
ENDDEFINE