Instrument Probe

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Modified by Admin on Sep 13, 2017

Parent Page: Objects

An Instrument Probe.

Summary

An instrument probe is a design directive. It instructs the system to connect the net to which it is attached directly to the monitoring instrument (e.g. a logic analyzer) without having to explicitly wire that net up through the design hierarchy to the sheet with the instrument on it.

Availability

Probes are available for placement in the Schematic Editor only, by choosing Place » Directives » Instrument Probe [P, V, I] from the main menus.

Placement

After launching the command, the cursor will change to a cross-hair and you will enter instrument probe placement mode.

Position the cursor over a wire or other net object and click or press Enter to effect placement.
Continue placing further instrument probe directives or right-click or press Esc to exit placement mode.

Additional Placement Actions

Press the Spacebar while in placement mode to rotate the instrument probe directive. Rotation is anti-clockwise and in steps of 90°.
Press the X or Y keys while in placement mode to flip the instrument probe directive along the X-axis or Y-axis respectively.

Any changes made to object properties during placement will cause the default properties for the object to be updated, unless the Permanent option - on the Schematic - Default Primitives page of the Preferences dialog - is enabled. When this option is enabled, changes made will affect only the object being placed and subsequent objects placed during the same placement session.

Connecting to the Instrument

Connecting to the instrument.

After placing an instrument probe directive at the point of interest, you need to define a value for its InstrumentProbe parameter. Enter a meaningful name for the probe point, for example the name of the associated net or the particular signal being monitored. Then, connect a wire to the required input of the monitoring instrument and attach a net label to the wire, the name of which is the same name you have defined for the InstrumentProbe parameter.

Non-Graphical Editing

The following three methods of non-graphical editing are available:

...via an associated properties dialog

This method of editing uses the following dialog to modify the properties of an instrument probe directive.

The Probe dialog.

The Probe dialog can be accessed prior to entering placement mode, from the Schematic - Default Primitives page of the Preferences dialog (Tools » Schematic Preferences). This allows you to change the default properties for the instrument probe directive, which will be applied when placing subsequent instrument probe directives.
During placement, the Probe dialog can be accessed by pressing the Tab key.
After placement, the Probe dialog can be accessed in one of the following ways:

double-clicking on the placed instrument probe directive
selecting the instrument probe directive and choosing Properties from the right-click pop-up menu
choosing the Change command from the Edit menu and then clicking once over the placed instrument probe directive.

...via the SCH Inspector panel

The SCH Inspector panel enables you to interrogate and edit the properties of one or more design objects in the active document. Used in conjunction with appropriate filtering, the panel can be used to make changes to multiple objects of the same kind, from one convenient location.

...via the SCH List panel

The SCH List panel allows you to display design objects from one or more documents in tabular format, enabling you to quickly inspect and modify object attributes. When used in conjunction with the SCH Filter panel, it enables you to display just those objects falling under the scope of the active filter - allowing you to target and edit multiple design objects with greater accuracy and efficiency.

Graphical editing

This method of editing allows you to select a placed instrument probe directive directly in the workspace and change its location graphically. Instrument probe directives are fixed with respect to their size and shape. As such, editing handles are not available when the instrument probe directive is selected:

A selected Instrument Probe.

Click anywhere inside the dashed box and drag to reposition the instrument probe directive as required. The instrument probe directive can be rotated or flipped while dragging.

If you attempt to graphically modify an instrument object that has its Locked property enabled, a dialog will appear asking for confirmation to proceed with the edit.
If the Protect Locked Objects option is enabled in the Schematic - Graphical Editing page of the Preferences dialog (Tools » Schematic Preferences), and the Locked option for this design object is enabled as well then this object cannot be selected or graphically edited.
You will have to double click on this locked object directly and disable the Locked property or disable the Protect Locked Objects option to graphically edit this object.

Notes

The instrument probe directive is essentially the same as the probe directive, but with the additional InstrumentProbe parameter. It is this parameter that turns it from being a simple probe into a means of monitoring any point in a design - connecting that point directly to the input line of a monitoring instrument.
If the instrument probe directive is placed on a net that connects to an FPGA pin, it can be used to monitor the status of that pin directly on the schematic sheet, as well as being used as an input source to a monitoring instrument. The former is achieved using the directive's ProbeValueDisplay parameter.

Instrument probe directive is placed on a net.

For this feature to function, the source FPGA design must be downloaded to the physical FPGA device and the associated JTAG Viewer panel for that device must be open and remain open.
The JTAG Viewer panel for a physical device is accessed by clicking the JTAG Viewer Panel button on the associated instrument panel for that device. The latter is loaded into the Instrument Rack - Hard Devices panel upon double-clicking the entry for the device, in the Hard Devices chain of the Devices view.

When an instrument probe is attached to a bus, the entire bus is taken up to the top-level sheet, irrespective of the name you assign to the InstrumentProbe parameter. When you add a net label to the input for the monitoring instrument, you must define the bus width required. For example, you may have attached an instrument probe to a bus with identifier Port1_Out[7..0] on a lower level sheet. The value for the InstrumentProbe parameter could be set to Port1_Out. The entire bus will be connected up to the sheet with the monitoring device (e.g. a LAX). Should you wish to wire up the entire bus as an input signal to the device, you would place a bus to the required input and add a net label of Port1_Out[7..0]. If you only wanted a particular signal or range of signals from the bus, you can define the width required in the attached net label.