how to pass value to crystal report parameter filed from the code

Question

I am creating crystal report like this:

Dim whereClass As String = ""

            sql = "SELECT * from v_LPO where PO_NUM = '" & txt_Po_No.Text & "'"
            ' where invoice_num='PI/2014/00001'"

            ds = New DataSet
            ds.Clear()
            ds.Tables.Clear()

            ds = Fn_Return_Dataset(sql)
            Dim slFilter As New SortedList
            slFilter.Clear()
            Dim objrpt As New frmrptengine(AppPath & "\reports\rptPurchaseOrder.rpt", ds)

            objrpt.machineName = machineName

            objrpt.Show()

in my rptPurchaseOrder.rpt i have a parameter field name PONAME. I want to pass manually value to my parameter field from the code? how i can do in this case?

any help is very appreciable..