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7 Programming with the »PLC Designer«

7.5 Creating remanent variables (retain/persistent)

Lenze · Controller | Parameter setting & programming · Reference Manual · DMS 1.5 EN · 04/2014 · TD17

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7.5.1 Storage of retain data on the SD card (only Controllers 3221 C/3231 C)

For Controllers 3221 C/3231 C, the values of the RETAIN variables are by default saved to the device

only.

•Use the L_Util_Retain function (from the L_Util.lib library) to save the RETAIN values to the SD

card of the controllers. Like this, the retain data can then be re-used, for instance after a device

replacement.

• RETAIN values saved to the SD card offer the benefit of subsequent use of these values after a

device replacement (subsequent use of the SD card).

L_Util_Retain

[7-1] Program example: Use of the L_Util_Retain function

When being called, the L_Util_Retain function saves the retain/persistent variables to the SD card

to file: retains.ret (directory: IPC\PLC).

 Note!

The SD card is only suitable for storing retain data if the RETAIN values do not change

very often.

• It is not possible to save the RETAIN values to the SD card during every PLC cycle.

• SD cards only have a limited number of write/read cycles. Thus, the retain variables

should not be saved at very short time intervals.

• Please avoid calling the L_Util_Retain() function in a motion task. The creation of the

RETAIN file prolongs the current PLC cycle of the calling task by several 100 ms.

•The functions SysSaveRetains() and SysRestoreRetains() provided in the

SysPlcCtrl23.Library are not supported and must not be used.

Function Library Function

L_Util_Retain() L_Util.library Save retain data to the SD card of the

controller.

PROGRAM PLC_PRG

VAR

FB_LUtilRetain: L_Util_Retain;

xRetainsIntoFile_LUtilRetain: BOOL;

instSetRetainValues: SetRetainValues;

xSetRetain: BOOL;

xStoreRetains_LUtilRetain: BOOL;

END_VAR

 Note!

Device replacement: Avoiding the loss of retain data

The L_Util_Retain function is only required for the Controllers 3221 C/3231 C.

•Use the L_Util_Retain function in the desired application in order to be able to re-use

the retain data, if required.

• In the event of a device replacement, the L_Util_Retain function must already have

been used in the application before, since otherwise the retain data are deleted.

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