The Restore parameter values after restart feature retains the online values of certain parameters in the controller's nonvolatile memory. In the event of a restart, the controller restores these values to controller RAM.
For accumulator-type parameter values, the restore parameter values feature may also restore the accumulator values after a user-initiated total download. However, if prior to the download, you select or clear the Restore parameter value after restart check box for one or more parameters, the accumulator values might not be restored for any of the modules in the associated controller. Use partial downloads when possible to preserve accumulator values. Note that the preserve critical block values feature provides additional protection for accumulator values.
Specific module-types and parameters that support the feature are listed later in this topic.
You enable the restore parameter values feature by selecting Restore parameter values after restart on the module that contains the parameters. For module level parameters, batch-input parameters, batch report parameters, and unit parameter definitions you must also enable the feature on the parameter properties. Function block parameters that support the restore feature do so automatically if the associated module is enabled to support the feature.
The following table shows the amount of space allocated for the restore parameter values after restart feature for controllers.
| Controller Type | Non-Volatile Memory Size |
|---|---|
| SD Plus and MD Plus | 380 KB |
| SX, MX, MQ, and SQ | 890 KB |
| SZ, PK | 1900 KB |
Consider the following to avoid exceeding these limits:
Each parameter using the restore feature uses 8 bytes of controller NVM
Each module enabled to support the restore feature uses 12 bytes of overhead
Function blocks may introduce additional overhead
To determine how much free NVM is available, check the controller's FreeNVM parameter in DeltaV Diagnostics.