FB_BA_WrtPersistDat

When activated, the function block FB_BA_WrtPersistDat first saves the persistent data in the Port_xxx.bootdata file. It is not necessary to explicitly specify the port or runtime system at which the PLC is located; this is determined internally. Once the data has been written, the content of the file Port_xxx.bootdata is copied to the backup file Port_xxx.bootdata-old. Thus both files are always synchronized. In case the original file with the persistent data is not readable, the backup copy, which is then read, contains the same data.

In any case, the checkmark "Clear Invalid Persistent Data" must be removed (see Description of persistent data handling under TwinCAT 3)

The function block can be started in two ways:

Via a positive edge at input bStt, if the function block is not in the set start-up phase.

Initially once the start-up phase is completed after a reset or TwinCAT restart. The duration is set at udiInitSttDly_sec in seconds. If "0" is entered there, the duration of the start-up phase is 0 and an initial execution of the function block is skipped.

No commands are accepted at bStt during the start-up phase.

If errors occur while reading, writing, opening or closing the files, this is indicated by a corresponding error message at bErr/sErrDescr. After an internally fixed waiting time of two seconds, the function block automatically attempts to execute the command (read, write, open or close) again.

It is therefore advisable to keep an eye on the error outputs or to evaluate them.

It is also important to note whether the backup file for the persistent data was loaded during the TwinCAT restart or after a reset. This indicates that the original file cannot be read and that the memory card of the controller is defective. It can be queried for each runtime system with the Boolean assignment of TwinCAT_SystemInfoVarList._AppInfo.OldBootData (see PlcAppSystemInfo).

Sample in ST:

Sample in CFC:

Description of persistent data handling under TwinCAT 3

TwinCAT saves the persistent data for each runtime system in a file during each orderly shutdown, i.e. when switching from Run to Config or Stop mode.

The file name consists of the ADS port name of the runtime system with the file extension .bootdata, e.g.: Port_851.bootdata and is stored in the TwinCAT directory under TwinCAT\3.1\Boot\PLC.

When the system is restarted, i.e. when switching to run mode, this file is read and then saved as Port_xxx.bootdata-old.

If the file Port_xxx.bootdata-old already exists, it is overwritten.

The original file Port_xxx.bootdata then no longer exists. It is created again automatically when switching to Stop mode or by the function block FB_WritePersistentData from the TC2_Utilities library.

This behavior applies to each runtime system; each system has its own files with persistent data.

If the file is defective when the TwinCAT system is restarted, the system automatically accesses the backup file Port_xxx.bootdata-old. However, this behavior only applies if the Clear Invalid Persistent Data checkmark is unchecked in the runtime settings. If it is checked and the original file is defective, no data will be read.

The Port_xxx.bootdata-old backup file is also used when the controller is de-energized. In this case, too, the current persistent data is not stored in Port_xxx.bootdata. When the system is restarted, only the old data is available, unless a more up-to-date file was created by the FB_WritePersistentData function block before the system was switched off.

VAR_INPUT

bStt                : BOOL;
udiInitSttDly_sec   : UDINT;

bStt: A rising edge at this input starts the function block if it is not in the start-up phase.

udiInitSttDly_sec: Start-up phase after a reset or TwinCAT restart. The duration is set in seconds. Once the start-up phase has elapsed, the function block is automatically started once. No commands are accepted at bStt during the start-up phase. If "0" is set at udiInitSttDly_sec, the start-up phase is skipped. This input is preconfigured with 10 s.

VAR_OUTPUT

bBusy                   : BOOL;
udiRemTiInitSttDly_sec  : UDINT;
bErr                    : BOOL;
sErrDescr               : T_MaxString;

bBusy: The function block is being executed.

udiRemTiInitSttDly_sec: Countdown of the set startup phase.

bErr: This output is switched to TRUE if the parameters entered are erroneous.

sErrDescr: Contains the error description.

Requirements