Loop in combination with Analog output

Question

Hi
I have modified the script thats translate a value in to a static analog output voltage. The value comes from another online running application. The analog output value must remain static until a new value arise. I'm using VB6 and DAQmx 8.5 on a XP computer. The DA converter is NI USB-6211. I have tried to play around with the Start/Stop and clear commands but my script still makes the program highly unstabile.
So am I using the commands correctly?. And have I setup the write commands correctly too. Can anyone allso explain how to use the command Doevent correctly
  Dim taskHandle As Long
    Dim clockEdge As Long
    Dim sampsPerCycle As Double
    Dim desiredSampleClockRate As Double
    Dim resultingFrequency As Double
    Dim amplitude As Double
    Dim numSampsPerChannel As Long
    Dim numChannels As Long
    Dim errorCode As Long
    Dim errorString As String
    Dim sampsPerChanWritten As Long
    Dim XICVolt As Double
 '  Create the DAQmx task.
    Call DAQmxCreateTask("", taskHandle)
    '  Add an analog output channel to the task and check to see whether there is only ONE task.
    Call DAQmxCreateAOVoltageChan(taskHandle, "Dev2/ao0", "aoChannel", "-10", "10", DAQmx_Val_VoltageUnits2_Volts, "")
    Call DAQmxGetTaskNumChans(taskHandle, numChannels)
    If numChannels > 1 Then
        errorCode = -1
        errorString = "Please specify only one channel."
        Err.Raise errorCode, , errorString
    End If
Data_is_recorded:
    If Actualcycles = expectedcycles Then
    GoTo end_script
    Else
    If Actualcycles > lastcycles Then
    DoEvents
     Call DataPoint.GetDataPoint(thenumberOfDataPoint, theXvalue, theYvalue)
        XICVolt = (theYvalue / 10000000#)
    '  Write to the desired channel(s).
    Call DAQmxWriteAnalogF64(taskHandle, 1, True, 10#, _
        DAQmx_Val_GroupByScanNumber, XICVolt, sampsPerChanWritten, ByVal 0&
    Else
     lastcycles = theWF.GetActualNumberOfCycles(sampleIndex, 0)
     End If
    GoTo Data_is_recorded
end_script:
End If
call DAQmx.stopTask(Taskhandle)
call DAQmx.clearTask(taskhandle)
Best regards
Peter

Answer 1

David Weber wrote:
thanks lot for all the great feedback. That's really helpful. I think I'll go for the NO_MERGE hint. A first test with this looks good.Keep in mind, only undocumented hint MATERIALIZE along with subquery factoring clause WITH (for which this hint was created) will work in real queries:
SQL> select my_id as id
  2       , my_id as same_id
  3  from (select /*+ NO_MERGE */ xxx_test_pkg.get_id(1) as my_id from dual),emp where rownum < 6;
        ID    SAME_ID
        20         20
        21         21
        21         21
        21         21
        21         21
SQL> select my_id as id
  2       , my_id as same_id
  3  from (select xxx_test_pkg.get_id(1) as my_id from dual where rownum=1),emp where rownum < 6;
        ID    SAME_ID
        22         22
        23         23
        23         23
        23         23
        23         23
SQL> select my_id as id
  2       , my_id as same_id
  3  from (select /*+ MATERIALIZE */ xxx_test_pkg.get_id(1) as my_id from dual),emp where rownum < 6;
        ID    SAME_ID
        24         25
        26         27
        28         29
        30         31
        32         33
SQL> with t as (select /*+ MATERIALIZE */ xxx_test_pkg.get_id(1) as my_id from dual)
  2  select my_id as id
  3       , my_id as same_id
  4  from t,emp where rownum < 6;
        ID    SAME_ID
        34         34
        34         34
        34         34
        34         34
        34         34
SQL> SY.