Timing between events

[Zenerdiode]

I'm using the Com port as a crude digital input device. I want to time between raising DSR and raising CTS; to an accuracy of 10ms. The time interval may be anything between one and 500 seconds. I'm trying to use the code below with timers to avoid burning CPU cycles but I'm losing track of what I'm doing(!)

Timer 2 and Timer 3 are set to 1ms.

#Region Timer
Sub TimeEvent
    Port.DTREnable=True
    WatchDog=HW.GetTickCount
    Timer2.Enabled=True
    Timer3.Enabled=True
End Sub

Sub Timer2_Tick
    If Port.DSR=True Then
        DSRtime=HW.GetTickCount
        Timer2.Enabled=False
        Return
    End If
    If (HW.GetTickCount-WatchDog)>500 Then
        Timer2.Enabled=False
        Timer3.Enabled=False
        Port.DTREnable=False
        Msgbox("DSR has not responded; check cable and connections.","Error",cMsgBoxOK,cMsgBoxHand)
    End If
End Sub

Sub Timer3_Tick
    If Port.CTS=True Then
        CTStime=HW.GetTickCount
        Timer3.Enabled=False
        Port.DTREnable=False
        Return
    End If
    If (HW.GetTickCount-WatchDog)>500000 Then
        Timer2.Enabled=False
        Timer3.Enabled=False
        Port.DTREnable=False
        Msgbox("CTS has not responded; Check cable and connections.","Error",cMsgBoxOK,cMsgBoxHand)
    End If
End Sub
#End Region

The time interval is then CTStime-DSRtime, but I don't know where to put it. Ideally, I would also like to be able to call the routine five times with a two second interval between, but because each sequence may be upto 500 seconds long, the CPU has to be free.

Am I missing the point here and be better using:

Do Until Port.DSR=True
    Sleep(1)
Loop

But that will lock into that loop for the duration; and I will not be able to update the elapsed time on screen (thats what I'm doing with Timer1)

I hope this makes sense as I'm tying myself in knots as I'm trying to get my problem across.

[Erel]

I'm not sure that I understood your program.
However 1ms interval is too short. The tick event is only fired when the cpu is free.
The events will be accumulated and not timed properly.

Can't you update the screen inside the 'Do until' loop?