SFC flags

SFC flags are implicitly generated variables with predefined names. You can use flags to influence the processing of an SFC chart. You can use these flags, for example, to display timeouts or reset step chains. In addition, you can activate jogging mode specifically to activate transitions. You have to declare and activate these variables in order to have access to them.

SFC flags

Name	Data Type	Description
`SFCInit`	`BOOL`	`TRUE`: CODESYS resets the sequence to the initial step. The other SFC flags are also reset (initialization). While the variable is `TRUE`, the initial step remains set (active), but its actions are not executed. Only when you set `SFCInit` again to `FALSE` is the POU further processed normally.
`SFCReset`	`BOOL`	Behaves similar to `SFCInit` However, CODESYS continues processing after the initialization of the initial step. For example, in the initial step, you could immediately reset the `SFCReset` flag to `FALSE`.
`SFCError`	`BOOL`	`TRUE` if a timeout occurs in an SFC chart. If second timeout occurs in the program, it is not registered unless you previously reset the variable `SFCError`. The declaration of `SFCError` is a requirement for other flag variables to function for controlling the chronological sequence (SFCErrorStep, `SFCErrorPOU`, `SFCQuitError`).
`SFCEnableLimit`	`BOOL`	Used specifically for activating (`TRUE`) and deactivating (`FALSE`) the timeout control in steps using `SFCError` If you declare and activate this variable (SFC settings), then you must set it to `TRUE` for `SFCError` to work. If you do not, then the timeouts are ignored. The is useful, for example, at start-up or in manual operation. If you do not declare the variable, then `SFCError` will work automatically. The requirement is the declaration of `SFCError`.
`SFCErrorStep`	`STRING`	Stores the name of the step that caused a timeout, which was registered by `SFCError` The name is kept until the registered step error is reset by means of `SFCQuitError` (FALSE -> TRUE). The requirement is the declaration of `SFCError`.
`SFCErrorPOU`	`STRING`	Stores the name of the block in which a timeout occurred and was registered by `SFCError`. The name is saved until the timeout is reset by `SFCQuitError`. The requirement is the declaration of `SFCError`.
`SFCQuitError`	`BOOL`	As long as this Boolean variable is `TRUE`, CODESYS pauses the processing of the SFC chart and any timeout, saved in the variable `SFCError`, is reset. If you reset the variable to `FALSE`, then all previous times in the active steps are reset. The requirement is the declaration of `SFCError`.
`SFCPause`	`BOOL`	As long as this variable is `TRUE`, CODESYS pauses the processing of the SFC chart.
`SFCTrans`	`BOOL`	`TRUE` when a transition is active
`SFCCurrentStep`	`STRING`	Shows the name of the active step, regardless of the time monitoring In parallel branches, the name of the step of the rightmost branch line is always stored.
`SFCTip`, `SFCTipMode`	`BOOL`	Controls the "jogging mode" of the SFC block If you enable this flag with `SFCTipMode=TRUE`, then you can activate the next step only by setting `SFCTip` to `TRUE`. While `SFCTipMode` is set to `FALSE`, transitions can also be used to continue activation.
`SFCErrorAnalyzation`,		Contains as string all variables that contribute to the total value `TRUE` of `SFCError` (timeout in one step) `SFCError` needs to be activated for this. `SFCErrorAnalyzation` implicitly uses the function of the POU `AnalyzeExpression` of the `Analyzation` library.
`SFCErrorAnalyzationTable`,		Contains in a table all variables that contribute to the total value `TRUE` of `SFCError` (timeout in one step) `SFCError` needs to be activated for this. `SFCErrorAnalyzationTable` implicitly uses the function of the POU `AnaylzeExpressionTable` of the `Analyzation` library.

Implicit generation of SFC flags

CODESYS declares SFC flags automatically when you activate the respective options. You can set this option in the SFC Settings tab of the properties dialog for each POU, or in the SFC project settings dialog for each SFC POU in the project.

Tip

The SFC settings for the SFC flags of individual POUs are effective only if you have not selected the Use defaults option. When you select this option, the settings apply that were defined in the project settings.

Tip

SFC flags that you declare in the SFC settings dialog are visible only in the online view of the SFC block.

Explicit generation of SFC flags

Manual declaration, which was necessary in CoDeSys V2.3, is now only required to enable write access from another block. In this case, you should note that when you declare the flag in a global variable list, you must deactivate its Declare setting in the SFC settings dialog. If you do not do this, then a local SFC flag is implicitly declared which CODESYS uses instead of the global variable.

Application examples for SFCError

Example 2. Example

You have created an SFC block named sfc1, which contains the s1 step. You have defined timeouts in the step properties. (See "Online view of sfc1 SFC POU" below.)

If for any reason the s1 step remains active longer than its time properties have permitted (timeout), then CODESYS sets the SFCError flag to permit access by the application.

To permit access, you have to declare and activate the SFC flag in the SFC settings. If you have only declared it, then the SFC flag is only displayed in the online view of sfc1 in the declaration part, but it has no function.

Now the SFC flag can be referenced within the POU, for example in an action (2) or outside of the block (1).

Online view of the SFC block sfc1

SFCError is TRUE as soon as a timeout occurs within sfc2.

Note that you can use the SFCErrorAnalyzation and SFCErrorAnalyzationTable flags (Analyzation library) to determine the components of the expression that contributes to the value TRUE of the SFCError.

Access to the flags

Syntax for access

You assign the flag directly within the POU: <variable name>:=<SFC flag>

Example 3. Example

checkerror:=SFCerror;

From another POU with POU name: <variable name>:=<POU name>.<SFC flag>

Example 4. Example:

checkerror:=SFC_prog.SFCerror;

If you need write access from another block, then you also have to declare the SFC flag explicitly as a VAR_INPUT variable in the SFC block or globally in a GVL.

Example 5. Example

Local declaration

PROGRAM SFC_prog
VAR_INPUT
  SFCinit:BOOL;
END_VAR

Global declaration in a global variable list

VAR_GLOBAL
  SFCinit:BOOL;
END_VAR

PROGRAM PLC_PRG
VAR
  setinit: BOOL;
END_VAR
SFC_prog.SFCinit:=setinit;  //Write access to SFCinit in SFC_prog