> For the complete documentation index, see [llms.txt](https://support.powerio.com/hub/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://support.powerio.com/hub/codesys-hvac/en/hvac-alarm-message-library/funktionsbausteine/fifo.md).

# FIFO

## `FIFO` (FB)

FUNCTION\_BLOCK FIFO

FIFO is a First-In First-Out memory with x storage locations for INT data. The two outputs xEmpty and xFull indicate when the memory is full or empty. The xReset input clears the entire contents of the memory. The FIFO is written with INT by applying TRUE to the xWrite input. A read command is executed by applying TRUE to xRead. Reading and writing can be performed simultaneously in one cycle. The block reads or writes in each cycle. The FIFO can be controlled via 3 methods: mRead, mWrite, mReset.

InOut:

| Scope  | Name           | Type           | Comment                              |
| ------ | -------------- | -------------- | ------------------------------------ |
| Input  | `iDataIn`      | `INT`          | Data to write into the FIFO          |
| Input  | `xRead`        | `BOOL`         | Read control                         |
| Input  | `xWrite`       | `BOOL`         | Write control                        |
| Input  | `xReset`       | `BOOL`         | Delete control                       |
| Input  | `aiFifoBuffer` | POINTER TO INT | FIFO with x slots                    |
| Output | `iDataOut`     | `INT`          | Data read from the FIFO              |
| Output | `xEmpty`       | `BOOL`         | xEmpty = TRUE means: memory is empty |
| Output | `xFull`        | `BOOL`         | FULL = TRUE means: memory is full    |
| Output | `diDataNumber` | `DINT`         | Number of data items in the FIFO     |


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