JK Flip-Flop (JKFF)

JK Flip-Flop (JKFF)

This information applies to the CompactLogix 5370, ControlLogix 5570, Compact GuardLogix 5370, GuardLogix 5570, Compact GuardLogix 5380, CompactLogix 5380, CompactLogix 5480, ControlLogix 5580, and GuardLogix 5580 controllers.
The JKFF instruction complements the Q and QNot outputs when the Clock input transitions from cleared to set.
Available Languages
Ladder Diagram
This instruction is not available in ladder diagram logic.
Function Block
JKFF_FBD_avail_v31
Structured Text
JKFF(JKFF_tag);
Operands
Function Block
Operand
Type
Format
Description
JKFF tag
FLIP_FLOP_JK
Structure
JKFF structure
FLIP_FLOP_JK Structure
Input Parameter
Data Type
Description
EnableIn
BOOL
Enable input. If cleared, the instruction does not execute and outputs are not updated.
Default is set.
Clear
BOOL
Clear input to the instruction. If set, the instruction
clears Q and sets QNot.
Clock
BOOL
Clock input to the instruction.
Default is cleared.
Output Parameter
Data Type
Description
EnableOut
BOOL
Indicates if instruction is enabled.
Q
BOOL
The output of the instruction.
QNot
BOOL
The complement of the Q output.
Structured Text
Operand
Type
Format
Description
JKFF tag
FLIP_FLOP_JK
Structure
JKFF structure
See Structured Text Syntax for more information on the syntax of expressions within structured text.
Description
When Clear is set, the instructions clears Q and sets QNot. Otherwise, if Clock is set and Clockn-1 is cleared, the instruction toggles Q and QNot.
The instruction sets Clockn-1 = Clock state every scan.
Affects Math Status Flags
No
Major/Minor Faults
None specific to this instruction. See
Common Attributes
 for operand-related faults.
Execution
Function Block
Condition/State
Action Taken
Prescan
EnableIn and EnableOut bits are cleared to false.
Tag.EnableIn is false
EnableIn and EnableOut bits are cleared to false.
Tag.EnableIn is true
EnableIn and EnableOut bits are set to true.
The instruction executes.
Instruction first run
Clockn-1 is set to 1.
Qn-1 is cleared to 0.
Instruction first scan
Previous input Clock states is set to True.
Previous output Q state is False.
Postscan
EnableIn and EnableOut bits are cleared to false.
Structured Text
Condition/State
Action Taken
Prescan
See Prescan in the Function Block table.
Normal Execution
See Tag.EnableIn is true in the Function Block table.
Postscan
See Postscan in the Function Block table.
Examples
When Clock goes from cleared to set, the JKFF instruction toggles Q. If Clear is set, Q is always cleared. The JKFF instruction sets QNot to the opposite state of Q.
Function Block
JKFF_FBD_ex_v31
Structured Text
JKFF_01.Clear := clear_input;
JKFF_01.Clock := clock_input;
JKFF(JKFF_01);
q_output := JKFF_01.Q;
qNot_output := JKFF_01.QNot;
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