in addition to what Viv wrote --

you send output to the control like this. (here i am
sending a character and waiting before the next, due to
requirements of the device i am controlling).

THISFORM.ole_MS_COMM.Output = CHR(148)
WAIT TIMEOUT 0.1 ''
THISFORM.ole_MS_COMM.Output = CHR(0)

and here is typical code in the OnComm event Viv mentioned.

LOCAL Received_Char
Received_Char = ' '

Received_Char = THISFORM.ole_MS_COMM.Input
* =MESSAGEBOX ( STR(ASC(Received_Char)) , 0 , 'Got a char' )

THISFORM.ole_MS_COMM.Output = CHR(0)

in this case, i need to reply with a null character in reponse
to every character i received.