Public Declare Function DF_Connect Lib "D:\my.dll" _
            Alias "MConnect" (ByVal Params as LPSTR, ByVal ErrorMsg As LPSTR) As Integer

Private Declare Function DF_Connect& Lib "uuuuuuuuu.aaa" _
    Alias "DFConnect" ( _
    ByRef Params As String, _
    ByRef ErrorMsg As String)

Idx = DF_Connect (param, errormsg)

'фунции из библиотеки mtesrl.dll
Private Declare Function DF_Connect Lib "mtesrl.dll" _
    Alias "MTEConnect" ( _
    ByVal Params As String, _
    ByVal ErrorMsg As String) As Integer

(C language definition)
int32 WINAPI MTEConnect(char *Params, char *ErrorMsg);


... вызов
int32 Idx;
char ErrorMsg[ 255 ];
...
Idx = MTEConnect(“PORT=COM1\rBAUDRATE= 115200 ”, ErrorMsg);
if( Idx < MTE_OK )
{
fprintf(stderr, “Ошибка при установке соединения: %s”, ErrorMsg);
	exit( 1 );
}
else 
  fprintf(stdout, “Соединение установлено.”);