LGF_FIFO (FB / 4.0.0)

Author: Siemens Industry Support

Short description

FIFO (First-In First-Out / Queue / ring buffer memory)
The function stores incoming data and outputs the oldest unprocessed data.

Block Interface


Bool	enable	valid	Bool
Bool	enable	valid	Bool
Bool	enqueue	busy	Bool
Bool	enqueue	busy	Bool
Bool	dequeue	error	Bool
Bool	dequeue	error	Bool
Bool	reset	status	Word
Bool	reset	status	Word
Bool	clear	elementCount	DInt
Bool	clear	elementCount	DInt
Variant	initialItem	isEmpty	Bool
Variant	initialItem	isEmpty	Bool
		isFull	Bool
		isFull	Bool
		diagnostics	LGF_typeDiagnostics
		diagnostics	LGF_typeDiagnostics
Variant	item		Variant
Variant			Variant
Variant	buffer		Variant
Variant			Variant

Input parameter

Identifier	Data type	Default value	Description
enable	Bool	FALSE	TRUE: Enable functionality of FB
enqueue	Bool	false	Enqueue item to the buffer
dequeue	Bool	false	Dequeue item from the buffer and return it on `item`
reset	Bool	FALSE	Initializing the buffer (reset the index and the counter)
clear	Bool	FALSE	Clearing the buffer and initialize with the initial value `initialItem` (Reset index and counter).
initialItem	Variant	---	Value with which the ARRAY of the buffer is initialized (usually: `0` / default value)

Output parameter

Identifier	Data type	Description
valid	Bool	TRUE: Valid set of output values available at the FB
busy	Bool	TRUE: FB is active and new output values can be expected
error	Bool	FALSE: No error TRUE: An error occurred during the execution of the FB
status	Word	16#0000-16#7FFF: Status of the FB 16#8000-16#FFFF: Error identification (see following Table)
elementCount	DInt	Number of elements in the buffer
isEmpty	Bool	TRUE: Buffer is empty
isFull	Bool	TRUE: Buffer is full
diagnostics	LGF_typeDiagnostics	Diagnostic structure to store and transfer diagnostic information from blocks through the interface.

In/Out parameter

Identifier	Data type	Description
item	Variant	The entry that is either returned from the ring buffer or written into the buffer
buffer	Variant	The ARRAY that is used as the ring buffer. (Array of…)

Status & Error codes

Code / Value	Identifier / Description
16#0000	STATUS_NO_ERROR Status: Execution finished without errors
16#7000	STATUS_NO_CURRENT_JOBS Status: No current jobs, initial state
16#7001	STATUS_FIRST_CALL First call after incoming new job (rising edge 'enable')
16#7002	STATUS_SUBSEQUENT_CALL Status: Subsequent call during active processing without further details
16#8001	ERR_BUFFER_EMPTY Error: The buffer is empty
16#8002	ERR_BUFFER_FULL Error: The buffer is full
16#8200	ERR_NO_ARRAY Error: No array is present at the input `buffer`
16#8201	ERR_WRONG_TYPE_ITEM Error: The data type of the InOut parameter `item` does not correspond to the data type of the array elements of the input `buffer`
16#8202	ERR_WRONG_TYPE_INITIAL_ITEM Error: The data type of the input `initialValue` does not correspond to the data type of the InOut parameter `item`
16#8203	ERR_BOOL_NOT_SUPPORTED Error: Boolean variables and arrays are not supported by `MOVE_BLOCK_VARIANT`. (Use a PLC Datatype instead)
16#8204	ERR_MULTIPLE_COMMANDS_DEDECTED Error: Multiple commands in the same cycle detected
16#8600	ERR_UNDEFINED_STATE Error: Due to an undefined state in state machine
16#8601	ERR_INDEX_IN_ARRAY_LIMITS_1 Error: The tag `statNextEmptyItemIndex` is not within the array limits
16#8602	ERR_INDEX_IN_ARRAY_LIMITS_2 Error: The tag `statFirstItemIndex` is not within the array limits
16#8610	ERR_CLEAR_BUFFER Error: While clearing buffer in block `MOVE_BLK_VARIANT` - check `subFunctionStatus` code
16#8611	ERR_RETURN_FIRST_ENTRY Error: While return first entry of buffer in block `MOVE_BLK_VARIANT` - check `subFunctionStatus` code
16#8612	ERR_REPLACE_ITEM_BY_INIT_VALUE Error: While replace item by initial value in block `MOVE_BLK_VARIANT` - check `subFunctionStatus` code
16#8613	ERR_WRITE_ENTRY Error: While write entry to buffer in block `MOVE_BLK_VARIANT` - check `subFunctionStatus` code

User defined datatype(s)

LGF_typeDiagnostics (UDT / V1.0.1)

Diagnostic structure to store and transfer diagnostic information from blocks through the interface.

Identifier	Data type	Default value	Description
status	Word	16#0000	Status of the Block or error identification when error occurred
subfunctionStatus	Word	16#0000	Status or return value of called FB's, FC's and system blocks
stateNumber	DInt	0	State in the state machine of the block where the error occurred

Functional description

NOTE: The status of called commands is output in subFunctionStatus. In this case, the output value in status indicates which command caused the error. In this case, refer to the TIA Portal Online Help section for information on the respective commands.

NOTE: In computer science, the queue is also based on the FIFO principle.

With the enqueue input, a new item is stored from the InOut parameter item in the next free position in the buffer. The output elementCount is incremented by one.

With the dequeue input, the next element to be processed is output to the InOut parameter item, and this field in the buffer is replaced by the value in the parameter initialItem. The output elementCount decremented by one.

With the reset input, the buffer is initialized, and the index and counter are reset. The elementCount output is set to zero and the isEmpty output is set to TRUE.

With the clear input, the buffer is emptied and initialized with the initial value initialItem. Index and counter are reset. The elementCount output is set to zero and the isEmpty output is set to TRUE.

Change log

Version & Date		Change description
	1.0.0	Siemens Industry Online Support
	19.08.2015	First released version
	1.0.1	Siemens Industry Online Support
	16.11.2015	Bug fix resetBuffer
	1.0.2	Siemens Industry Online Support
	02.01.2017	Upgrade: TIA Portal V14 Update 1
	1.0.3	Siemens Industry Online Support
	17.08.2018	Upgrade: TIA V15 Update 2
	1.0.4	Siemens Industry Online Support
	23.11.2018	Upgrade: TIA V15.1
	2.0.0	Siemens Industry Online Support
	29.01.2019	Output "done" removed (not necessary, because block works synchronous)
	3.0.0	Simatic Systems Support
	22.10.2019	Code refactoring, comments added Interface change (enqueue, dequeue etc.) Set version to V3.0.0, harmonize the version of the whole library
	3.0.1	Simatic Systems Support
	15.02.2021	Insert documentation
	4.0.0	Simatic Systems Support
	04.09.2024	Rework to PLC Open `Enable` behavior Add `isFull` outputs Fix Bug while filling after left shift operation Rework to diagnostic output datatype