F_TRIG

Function Block - Falling pulse detection

Inputs

CLK : BOOL Boolean signal

Outputs

Q   : BOOL TRUE when the input changes from TRUE to FALSE

Truth table

CLK

CLK prev

Q

0

0

0

0

1

1

1

0

0

1

1

0

Remarks

Although ]P[ an ]N[ contacts may be used in LD language, it is recommended to use declared instances of R_TRIG or F_TRIG function blocks in order to avoid unexpected behaviour during an On Line change.

ST Language

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

FBD Language

F_TrigFbd.GIF (1207 octets)

LD Language

(* the input signal is the rung - the rung is the output *)
F_TrigLd.GIF (1299 octets)

IL Language:

(* MyTrigger is declared as an instance of F_TRIG function block *)
Op1: CAL MyTrigger (CLK)
     LD  MyTrigger.Q
     ST  Q

See also

R_TRIG