If I understand you good, you can use hbcomm for serial communication.
There is a piece of my code for opening COM port, sendig and receiveing data :

	cPortName := "COM1"
	nBaud := 9600
	oWinPort := win_com():Init(cPortName, nBaud, NOPARITY, 8, ONESTOPBIT)
	
    if !oWinPort:Open
        msgstop("Error opening COM port!" )
		return .F.
    else
        // COM port opened successfully
		oWinPort:QueueSize( 1000, 1000 )
		oWinPort:Purge()
		//TimeOuts( nReadInterval, nReadMultiplier, nReadConstant, nWriteMultiplier, nWriteConstant )
		oWinPort:Timeouts(1500,1000,20000,1000,20000)
		
		// set control of communication flow
        oWinPort:RTSFlow(.t.)
        oWinPort:DTRFlow(.t.)
        oWinPort:XonXoffFlow(.t.)
		
		// set modem lines states
		
        oWinPort:SetDTR(.t.)
        oWinPort:SetDTR(.t.)
        oWinPort:SetRTS(.t.)
    endif


now you can use this function to send data:

	oWinPort:Write("any string to send via COM Port")

and this function for read data from serial port


	cAnswer := ""
	oWinPort:Read(@cAnswer, nNumberOfBytesToRead)


I've placed two useful functions below:

function ECR_ComClose
	local nCount := 0, cAnswer := ""
	
	if oWinPort <> NIL
		oWinPort:QueueStatus( , , , , , @nCount,  )
		oWinPort:Read(@cAnswer, nCount)
		oWinPort:Purge()
		oWinPort:RTSFlow(.f.)
		oWinPort:DTRFlow(.f.)
		oWinPort:XonXoffFlow(.f.)
		oWinPort:SetDTR(.f.)
		oWinPort:SetDTR(.f.)
		oWinPort:SetRTS(.f.)
		oWinPort:Close()
	endif
	oWinPort := NIL
return .t.

function ECR_CalcCRC 
	param buff
	local i, crc, Result, cChar

	crc := 0
	for i := 1 to Len(buff)
		cChar := asc(substr(buff,i,1))
		cChar := NumRol(cChar,(i - 1)%9)
		crc := NumXor(crc,cChar)
		Result := NtoC (crc, 16,4,"0")
	next i
 return Result