NOVRAM
CX9020
43
Version: 2.0
8.1
Use under TwinCAT 3
Under TwinCAT 3 (from Build 4020) a delta algorithm is used to save data in the NOVRAM. The algorithm
does not save all the variables in the NOVRAM. Instead, it searches for changes (delta function) compared
to the previous cycle and only saves variables that have changed.
To use the delta algorithm, a Retain Handler must be created in TwinCAT 3, and the relevant variables must
be declared in the PLC with the keyword VAR_RETAIN.
A new feature of this method is that no function blocks have to be used. The Retain Handler saves data in
the NOVRAM in the event of a power failure and makes them available again once the power has been
restored.
8.1.1
Creating a Retain Handler
This chapter describes how to create a Retain Handler in TwinCAT 3. The Retain Handler saves data in the
NOVRAM and makes them available again. In other words, important variable values such as production
data or counter values are retained during a restart or power failure.
Prerequisites for this step:
• TwinCAT 3.1 Build: 4020.
• A target device selected in TwinCAT.
Create the Retain Handler as follows:
1. Right-click on
Devices
in the tree view on the left-hand side.
2. In the context menu click on
Scan
.
3. Select
Device (NOV-DP-RAM)
and confirm with
OK
.
4. Click on
Yes
to search for boxes.
Summary of Contents for CX9020
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