Hello,

I'm trying to start logging a series of tags cyclically while a specific bit in the PLC is on, and stop logging when the bit turns off.  This is relatively easy using HMI pushbuttons, but when attempting to use the function "StartLogging" on a Value Change Event of an HMI bool variable, it doesn't seem to work. Using WinCC Advanced, S7-1200, and TP700. 

Is there a way to do this?

Thanks,

The bit/tag I'm using in the event "value change" are external. However, the bit is coming from the PLC, and not from an IO field.

Can someone suggest a way to do what I'm trying to accomplish?

Thank you Ohjus.

I've set the tag to cyclic continuous, but don't fully understand the proper syntax in the VB Script.

I've created a new VB function:

If LogStartTrigger = True Then
StartLogging hmiDataLog,TestLog
Else
StopLogging hmiDataLog,TestLog
End If

The name of my log is TestLog.  However, it isn't recognizing it

Error: (,A VB_Script or HMI_Tag object named 'TestLog' was not found in line 11, Column 25,,,4:32:53 PM)

The log works fine on the panel using pushbuttons.

Also, do I need to add this function under "Scheduled Tasks" or will it execute automatically on runtime? If so, what do I set the trigger to?

Thanks for the help.

Exactly what I was looking for.

Amazing I spent hours pouring through the help and manuals and couldn't find the simple syntax or procedure to achieve this relatively common task.

Many thanks to you sir.

Quick additional question if I may: 

What if the log starting tag is a bit in a word in the HMI tag table as opposed to a bool variable, what is the syntax in the VB function?

For bit 0, something along the lines of:

If LogTagWord & 0x0001 = 0x0001 Then?

Thanks

The logtagWord is in an optimized DB, although not sure what difference this makes.

In both cases the tag is an HMI Tag linked to a PLC tag, so not sure why it makes a difference how the PLC sees it.

I'm just asking about the proper VB syntax using a word in this case.