Read I/O Function

LabVIEW 2018 FPGA Module Help

Edition Date: March 2018
Part Number: 371599P-01
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Owning Palette: User-Controlled I/O Sampling Functions

Requires: FPGA Module

Reads the I/O data from the I/O items. This function waits for new I/O data to become available through the Generate I/O Sample Pulse Method function.

The following connector pane displays the parameters that appear when this function is outside a single-cycle Timed Loop.


error in describes error conditions that occur before this node runs. This input provides standard error in functionality. If error in does not equal No Error, the value of error in passes to error out and this function does not execute.
FPGA I/O In is an optional input that allows you to specify the FPGA I/O item to read or write using an FPGA I/O control or constant. To use an FPGA I/O control as a connector pane input, the FPGA VI must be configured for reentrant execution.
Timeout specifies the maximum time, in number of clock ticks, that the function waits for new data to become available from all I/O items. A value of –1 prevents the function from timing out, so the function waits indefinitely for new data to become available. If Timeout is 0 and this function cannot read data immediately, a timeout occurs.
Ready for Output specifies whether downstream nodes are ready for this node to return a new value. The default is TRUE. Use a Feedback Node to wire the Ready for Input output of a downstream node to this input of the current node.
Note  If this terminal is FALSE during a given cycle, the output valid terminal returns FALSE during that cycle.
To display this terminal, right-click the function and select Inside single-cycle Timed Loop from the shortcut menu.
error out contains error information. This output provides standard error out functionality.
FPGA I/O Out returns the FPGA I/O In.
I/O Item is the data read from the FPGA I/O item.

When you select an element on the node without wiring a value to FPGA I/O In, the name of this parameter changes to match the name of the FPGA I/O item you specify.
Timed Out returns TRUE if this method has timed out. If Timed Out is TRUE, no data was read from any I/O items.
Output Valid returns TRUE if this node has computed a result that downstream nodes can use. Wire this output to the Input Valid input of a downstream node to transfer data from the node to the downstream node.

To display this terminal, right-click this function and select Inside single-cycle Timed Loop from the shortcut menu.

Read I/O Details

To select a method, first configure the node with an I/O item.

Not all targets support the User-Controlled I/O Sampling functions.

If multiple Read I/O Method functions contain the same I/O item, all functions reference the same data buffer. A read from any function will return the oldest unread data, and data that the Generate I/O Sample Pulse Method function acquires will overwrite the oldest element in the buffer. If the node contains multiple I/O items, this node reads data only if each I/O item has unread data available for reading.

Single-Cycle Timed Loop Support

This node is supported inside and outside the single-cycle Timed Loop if the target supports it. Right-click the function and select Execution Mode»Outside single-cycle Timed Loop or Inside single-cycle Timed Loop to specify where the function executes.

Error Handling Details

You can use the error terminals to place this node in the data flow of the VI as well as to ensure the data you receive is valid. FPGA targets might report errors differently. Refer to the specific FPGA target hardware documentation for information about how specific FPGA targets report errors.


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