如题，我用S7ProSim正常连接PLCSIM后，用以下的代码读取Q通道里的数据，但发现无法读取QD的数据，不知是为何，手册中说是可以读的，希望各位大侠指点。
=====================================================================
部分代码：
Private Sub ReadQImageCMD_Click()
Dim rQ
S7ProSim1.ReadOutputImage 0, 1, S7_Byte, rQ
LogText.Text = Now & ": QB0=" & Hex(rQ(0)) & vbCrLf & LogText.Text
S7ProSim1.ReadOutputImage 0, 1, S7_Word, rQ
LogText.Text = Now & ": QW0=" & Hex(rQ(0)) & vbCrLf & LogText.Text
S7ProSim1.ReadOutputImage 0, 1, S7_DoubleWord, rQ
LogText.Text = Now & ": QD0=" & Hex(rQ(0)) & vbCrLf & LogText.Text
S7ProSim1.ReadOutputPoint 0, 1, S7_Byte, rQ
LogText.Text = Now & ": QB0=" & Hex(rQ) & vbCrLf & LogText.Text
S7ProSim1.ReadOutputPoint 0, 1, S7_Word, rQ
LogText.Text = Now & ": QW0=" & Hex(rQ) & vbCrLf & LogText.Text
S7ProSim1.ReadOutputPoint 0, 1, S7_DoubleWord, rQ
LogText.Text = Now & ": QD0=" & Hex(rQ) & vbCrLf & LogText.Text
End Sub
---------------------------------------------------------------------
显示结果：
2009-10-7 20:58:55: QD0=0
2009-10-7 20:58:55: QW0=8700
2009-10-7 20:58:55: QB0=87
2009-10-7 20:58:55: QD0=0
2009-10-7 20:58:55: QW0=8700
2009-10-7 20:58:55: QB0=87
=====================================================================