Attention

IronPLC can only run very simple programs. The steps described are accurate but many language features are not yet supported.

SR

Set-dominant bistable function block. A flip-flop where the set input takes priority: if both S1 and R are TRUE, the output Q1 is TRUE.

IEC 61131-3	Section 2.5.2.3.1
Support	Not yet supported

Inputs

Name	Type	Description
S1	BOOL	Set input (dominant)
R	BOOL	Reset input

Outputs

Name	Type	Description
Q1	BOOL	Output state

Behavior

The output Q1 is set to TRUE when S1 is TRUE, and reset to FALSE when R is TRUE. Because the set input is dominant, if both S1 and R are TRUE simultaneously, the output Q1 is TRUE. The output retains its value between scans.

Example

VAR
  latch1 : SR;
  set_signal : BOOL;
  reset_signal : BOOL;
  output : BOOL;
END_VAR

latch1(S1 := set_signal, R := reset_signal);
output := latch1.Q1;

See Also

• RS — reset-dominant bistable