Convert The Value Returned By Reference Into Byte ()?

I have a DLL that is written in C++. the functions of the DLL have parameters defined as unsigned char:

apiStatus __declspec(dllexport) __stdcall Gen2Read(HANDLE

hCom,unsigned char Membank,unsigned char WordPtr,unsigned char WordCnt, unsigned char *value, unsigned char ReaderAddr );

I have tried

<DllImport("Mr915ApiV10.dll", CharSet:=CharSet.Auto)> _

Public Function Gen2Read(ByVal hComHandle As IntPtr, ByVal Membank As Byte, ByVal WordPtr As Byte, ByVal WordCnt As Byte, ByRef value As IntPtr, ByVal ReaderAddr As Byte) As Integer
End Function

And the call:

Gen2Read(hComHandle, membank, wordptr, wordcnt, value, m_ReaderAddres)

In the original code in c + + value is: unsigned char buf [40]. And I'm not able to convert the value returned by reference into Byte ().