使用ado,如何调用oracle pl/sql块并指定输入/输出绑定变量(参数?)

我试图用ado和vba调用pl/sql块,但是我不能传递输入和/或输出绑定变量(可能是aka参数)。

dim cn as ADODB.connection
' ... open connection ...

dim plsql as string

plsql =         "declare"
plsql = plsql & "  num_in  number := ?;"
plsql = plsql & "  num_out number; "
plsql = plsql & "begin"
plsql = plsql & "  num_out := num_in * 5;"
plsql = plsql & "  ? := num_out;"
plsql = plsql & "end;"

dim cm as ADODB.command
set cm = new ADODB.command
set cm.activeConnection = cn
cm.commandText = plsql
cm.commandType = adCmdText

cm.parameters.append cm.createParameter(, adDouble, adParamInput,, 5)
cm.parameters.append cm.createParameter(, adDouble, adParamOutput   )

cm.execute  ' FAILS HERE

msgBox(cm.parameters(2))

上面的代码片段在 cm.execute 线与 ORA-01008:并非所有变量都绑定

如果有人帮我解决问题,我将不胜感激。