f_trig

 Function Block A function block groups an algorithm and a set of private data. It has inputs and outputs. - Falling pulse detection.

Inputs

Input	Data Type	Range	Unit	Default	Description
CLK	BOOL				Boolean signal.

Outputs

Output	Data Type	Range	Unit	Description
Q	BOOL			TRUE when the input changes from TRUE to FALSE.

Remarks

• It is recommended to use declared instances of R_TRIG or F_TRIG function blocks.
  • This is to avoid contingencies during an Online Change Applies to downloading PLC code changes while the applicaiton is running..

Truth Table

CLK	CCLK (prev)	Q
0	0	0
0	1	1
1	0	0
1	1	0

FBD Language Example

FFLD Language Example

• In the FFLD "Free Form Ladder Diagram" Language, ]P[ and ]N[ contacts can be used.

IL Language Example

(* MyTrigger is declared as an instance of F_TRIG function block *)
Op1: CAL MyTrigger (CLK)
LD "Ladder diagram"
Ladder logic is a method of drawing electrical logic schematics. It is now a very popular graphical language for programming Programmable Logic Controllers (PLCs). It was originally invented to describe logic made from relays. The name is based on the observation that programs in this language resemble ladders, with two vertical "rails" and a series of horizontal "rungs" between them  MyTrigger.Q
ST  Q

ST Language Example

(* MyTrigger is declared as an instance of F_TRIG function block. *)
MyTrigger (CLK);
Q := MyTrigger.Q;

See Also

r_trig