LIFO Load (LFL)

The LFL instruction copies the Source value to the LIFO.

Use the LFL instruction with the LFU instruction to store and retrieve data in a last-in/first-out order. When used in pairs, the LFL and LFU instructions establish an asynchronous shift register.

Typically, the Source and the LIFO are the same data type.

When enabled, the LFL instruction loads the Source value into the position in the LIFO identified by the .POS value. The instruction loads one value each time the instruction is enabled, until the LIFO is full.

IMPORTANT: You must test and confirm that the instruction does not change data that you don’t want it to change.

The LFL instruction operates on contiguous data memory.

Available Languages

Ladder Diagram

Operands

There are data conversion rules for mixed data types within an instruction.

Ladder Diagram

Operand	Type	Format	Description
Source	SINT INT DINT REAL String type structure	immediate tag	Data to be stored in the LIFO.
LIFO	SINT INT DINT REAL String type structure	array tag	LIFO to modify Specify the first element of the LIFO
Control	CONTROL	tag	Control structure for the operation Typically use the same CONTROL as the associated LFU
Length	DINT	immediate	Maximum number of elements the LIFO can hold at one time
Position	DINT	immediate	Next location in the LIFO where the instruction loads data Initial value is typically 0

CONTROL Structure

Mnemonic	Data Type	Description
.EN	BOOL	The enable bit indicates the LFL instruction is enabled.
.DN	BOOL	The done bit is set to indicate that the LIFO is full (.POS = .LEN). The .DN bit inhibits loading the LIFO until .POS < .LEN.
.EM	BOOL	The empty bit indicates the LIFO is empty. If .LEN < or = to 0 or .POS < 0, the .EM bit and .DN bits are set.
.LEN	DINT	The length specifies the maximum number of elements the LIFO can hold at one time.
.POS	DINT	The position identifies the location in the LIFO where the instruction will load the next value.