# LGF_FIFO (FB / 4.0.0)

Overview

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

| LGF_FIFO (FB) |
--- | --- | ---
Bool |  |  | enable |  | valid |  |  | Bool
Bool |  |  | enqueue |  | busy |  |  | Bool
Bool |  |  | dequeue |  | error |  |  | Bool
Bool |  |  | reset |  | status |  |  | Word
Bool |  |  | clear |  | elementCount |  |  | DInt
Variant |  |  | initialItem |  | isEmpty |  |  | Bool
|  |  |  |  | isFull |  |  | Bool
|  |  |  |  | diagnostics |  |  | LGF_typeDiagnostics
Variant |  |  | item |  |  | Variant
Variant |  |  | buffer |  |  | 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