Table Of Contents

Read FIFO (Clock-Driven Logic)

Last Modified: January 12, 2018

Reads and removes the oldest element from the FPGA FIFO.

Programming Patterns

Transferring Data between Clock Domains Using FIFOs

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reference in

A reference to the FIFO to read from.

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error in

Error conditions that occur before this node runs.

The node responds to this input according to standard error behavior.

Standard Error Behavior

Many nodes provide an error in input and an error out output so that the node can respond to and communicate errors that occur while code is running. The value of error in specifies whether an error occurred before the node runs. Most nodes respond to values of error in in a standard, predictable way.

error in does not contain an error error in contains an error
If no error occurred before the node runs, the node begins execution normally.

If no error occurs while the node runs, it returns no error. If an error does occur while the node runs, it returns that error information as error out.

If an error occurred before the node runs, the node does not execute. Instead, it returns the error in value as error out.

Default: No error

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ready for output

Boolean value that specifies whether downstream nodes are ready for this node to return a new value.

Use Feedback Node to wire ready for input of a downstream node to ready for output of the current node. If this input is False during a given cycle, output valid returns False during that cycle.

True The downstream node is ready for the next data point.
False The downstream node is not ready for the next data point.

Default: False

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reference out

A reference to the FIFO that was read from.

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data

The oldest data element in the FIFO. If the FIFO is empty, the returned element is undefined.

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error out

Error information.

The node produces this output according to standard error behavior.

Standard Error Behavior

Many nodes provide an error in input and an error out output so that the node can respond to and communicate errors that occur while code is running. The value of error in specifies whether an error occurred before the node runs. Most nodes respond to values of error in in a standard, predictable way.

error in does not contain an error error in contains an error
If no error occurred before the node runs, the node begins execution normally.

If no error occurs while the node runs, it returns no error. If an error does occur while the node runs, it returns that error information as error out.

If an error occurred before the node runs, the node does not execute. Instead, it returns the error in value as error out.
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output valid

Boolean value that indicates whether this node computes a result that downstream nodes can use.

Wire this output to input valid of a downstream node to transfer data from the node to the downstream node.

True Downstream nodes can use the result this node computes.
False This node returns an undefined value that downstream nodes cannot use.
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Note  

This node may return different undefined values when executed in simulation mode versus when executed on hardware.

Where This Node Can Run:

Desktop OS: none

FPGA: All devices

Web Server: Not supported in VIs that run in a web application


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