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Data Transfer from Safety Program to Standard User Program

The standard user program can read out all of the data from the safety program, for example, through symbolic (fully qualified) access to the following:

• Instance DBs of the F-FBs

• F-DBs (for example, "Name F_DB".Signal_1)

• Process input image and the process output image of F-I/O (for example, "Emergency_Stop_Button_1" (E 5.0) )

Note

The process input image for F-I/O is updated not only at the start of an F runtime group before execution of the F-program block, but also by the standard operating system.

To find out the time at which the process input and output images are updated by the standard operating system, refer to "Process image of inputs/outputs" in the online Help for STEP 7. With the S7-400, bear in mind the update timing when using process image partitions. For this reason, when accessing the process input image for F- I/O in the standard user program, you can obtain different values than in the safety program. The differing values can occur due to:

• Different update timing

• Use of fail-safe values in the safety program

To obtain the same values in the standard user program as in the safety program, you can therefore only access the process input image in the standard program after execution of an F-runtime group. In this case, you can also evaluate the QBAD variable in the relevant F-I/O DB in the standard user program to find out whether the process input image contains fail-safe values (0) or process data. When using process image partitions (S7-400 only), make sure as well that the process image is not updated by the standard operating system or by SFC 26 UPDAT_PI between execution of an F-runtime group (F-CALL) and evaluation of the process input image in the standard user program.

F-Shared DB

In the standard user program or on an operator control and monitoring system, you can read out the following information in the F-shared DB:

• Operating mode: safety mode or deactivated safety mode ("MODE" variable) • Error information "Error occurred when executing safety program" ("ERROR"

variable)

• Collective signature of the safety program ("F_PROG_SIG" variable) • Compile data of the safety program ("F_PROG_DAT" variable,

DATE_AND_TIME data type)

You use fully qualified access to access these variables (e.g.,

"F_GLOBDB".MODE). The number and symbolic name of the F-shared DB and the absolute address of the variables are indicated in the printout of the safety

program.

Note

Starting with S7 Distributed Safety V 5.2, the collective signature of the safety program ("F_PROG_SIG" variable) is output in the F-shared-DB as a double word. If you previously used S7 Distributed Safety V 5.1 and read out the

"F_PROG_SIG" variable in the safety program or by means of an operator control and monitoring system and you now convert to S7 Distributed Safety

V 5.3, you must change the data type to DWORD for evaluation, if necessary.

!

Do not copy the F-shared DB from a safety program to another safety program (exception: copying the entire S7 program).

Memory Marker

You can also write memory bits into the safety program to enable intermediate results of the safety program to be used by the standard user program without having to pass through fail-safe data blocks. However, these markers cannot be read in the safety program itself.

Process Output Image

In the safety program, you can also write to the process output image (PIQ) of standard I/O, for display purposes, for example. These values cannot be read in the safety program, either (see also table of supported address areas in

Differences between the Programming Languages F-FBD/F-LAD and the Standard Languages FBD/LAD).

Data Transfer from Standard User Program to Safety Program

Only fail-safe data or fail-safe signals from fail-safe I/O and other safety programs (in other F-CPUs) can be generally be processed in the safety program, since standard data and signals are not safe.

If you nevertheless have to process data from the standard user program in the safety program, you can evaluate either memory bits from the standard user program or the process input image (PII) of standard I/O in the safety program (see also table of supported address areas in Differences between the F-FBD/F-LAD Programming Languages and the Standard FBD/LAD Languages).

!

Because these data are not generated safely, you must carry out additional process-specific validity checks in the safety program to ensure that no dangerous states can arise. If a memory bit or input of standard I/O is used in both F-runtime groups, you must perform the validity check separately in each F-runtime group.

To facilitate the checks, all signals from the standard user program that are evaluated in the safety program are expressed when the safety program is printed out.

Note

Data from the standard user program (bit memory or PII of standard I/O) cannot be used for edge memory bits of the RLO Edge Detection (N, P) or Address Edge Detection (NEG, POS) instructions or for the address of the Flip Flop (SR, RS) instructions, since these data are read and written to by the instruction.

Note

In the FBD/LAD editor, all addresses that are not fail-safe are shown by default with a yellow background when F-blocks are edited in F-FBD/F-LAD.

Programming Validity Checks

Examples:

• Use comparison instructions to check whether unsafe data from the standard user program exceed or fall below permitted upper and lower limits. You can then influence your safety function with the result of the comparison.

• Only allow a motor to be switched off, but not to be switched on, with unsafe signals from the standard user program, for example, using Set, Reset, or Flip- flop instructions.

• For starting cycles, gate unsafe signals from the standard user program, for example, using AND-gating with starting conditions that you derive from fail- safe signals.

If you want to process unsafe data in the safety program, bear in mind that a sufficiently simple method of checking validity does not exist for all unsafe data.

Reading Data from the Standard User Program that Can Change during Runtime of an F-Runtime Group

You must use dedicated memory bits if, in the safety program, you want to read data from the standard user program (bit memory or PII of standard I/O) and these data can be changed by the standard user program or an operator control and monitoring system during runtime of the F-runtime group in which the data are read - for example, because your standard user program is being executed by a higher priority cyclic interrupt. You must write the data from the standard user program to these memory bits immediately before calling the F-runtime group. You can then only access these memory bits in the safety program.

Note, too, that clock bit memory that you defined when configuring your F-CPU (in HW Config, in the Object Properties dialog box of the F-CPU) can change during runtime of the F-runtime group, since clock bit memory runs asynchronously to the F-CPU cycle.

Note

If you do not take into account the information provided above, the F-CPU can go to STOP mode. One of the following diagnostics events will then be entered in the diagnostics buffer of the F-CPU:

• "Data corruption in the safety program prior to output to F I/O"

• "Data corruption in the safety program prior to output to partner F-CPU" • "Safety program: internal CPU fault; internal error information: 404"