Short summary

Name	`F_TRIG`
→POU type	→function block
Category	IEC-block, Edge
Conform to →IEC-standard	behavior according to "Technical Report" (see below)
Graphical interface
Available since	version 1.18.0 (for logi.CAD 3)

Functionality

This block detects a falling edge.

→Turning input CLK off triggers output Q to return value TRUE (or an equivalent) from one execution of the function block to the next. Output Q returns value FALSE (or an equivalent) at the next execution .

Observe:

If the input CLK is connected to value FALSE, output Q returns FALSE from its first execution onward following a →cold restart. This behavior has been implemented according to Technical Report IEC TR 61131-8 (Programmable controllers – Part 8: Guidelines for the application and implementation of programming languages).

In-/outputs

	Identifier	→Data type	Description
Inputs:	`CLK`	`BOOL`	current value
Outputs:	`Q`	`BOOL`	flag showing falling edge detection

Input EN and output ENO are available when →calling the block. See "Execution control: EN, ENO" for information on input EN and output ENO.

See:

"Blocks for safe logic" whether this block is supported for developing safety-relevant applications.
"Highlighting safe logic in the FBD-editor" for the effects when using the block as a block for safe logic .

Example for usage within ST-editor

PROGRAM Test
  VAR
    Activator : F_TRIG;
    Out       : BOOL;
    Trigger   : BOOL;
  END_VAR
 
  Activator(CLK := Trigger, Q => Out);
  (* Instance of block 'F_TRIG' is called. *)
  (* Input 'CLK' gets value from 'Trigger' variable. *)
  (* Output 'Q' returns TRUE for one cycle, if 'Trigger' was set to FALSE. *)
  (* Variable 'Out' accesses the output 'Q'. *)
END_PROGRAM

When creating your application within the ST-editor, enter a call of a block by typing the text as requested by the syntax or use Content Assist.