Digital Scope

Use the digital scope to view a graph of the expected waveform underneath the actual waveform using the pattern, timing set, and levels, including compare strobe locations, V_OH and V_OL levels, and expected drive levels. You can use the digital scope to help debug failures to verify that the actual waveform accurately reflects what you expect based on what the pattern and timing define.

Note  

The cycles or vectors on which you generate digital scope waveform points must be repeatable for every burst of the pattern. Using opcodes that result in non-deterministic pattern execution, such as using conditional jumps based on the failed or matched state of the pattern, can result in errors and potentially inaccurate results. Remove the pins with such compares from the pin list for the digital scope to avoid such inaccuracies. For example, if you configure the digital scope to start at a cycle, all cycles in the range you specify must always be at the same vectors on every burst. If you configure the digital scope to start at a vector, that vector does not have to always execute on the same cycle, but the number of cycles you specify to plot after the start vector cycle for each burst must correspond to the same vectors on every burst.

Launching the Digital Scope

Use the following techniques to launch the digital scope:

• Select View»Digital Scope.
• Click the Show Digital Scope button on the pattern document toolbar.
• Right-click a cell in the pattern document and select Use Digital Scope on Selected Pins Data from the context menu.
• After you burst a pattern, right-click a cell in the History RAM View and select Use Digital Scope on Selected Pins Data from the context menu.

Running the Digital Scope

Use the Run Digital Scope and Abort buttons on the toolbar to control the operation.

Note  

When you run the Digital Pattern Editor in demo mode and execute a digital scope operation, the generated results reflect the actual pin states from the target pattern and the currently active timing values but do not reflect a realistic execution of patterns. Use the pattern waveform view to see a graph of the pattern without requiring the use of digital pattern instruments.

Reading the Digital Scope

The digital scope graph can contain the following components:

• Sampled Point — Indicates a particular sample. These points disappear if the number of samples available provides a sufficient resolution to draw a smooth signal.
• Non-Converging Point — Indicates a particular sample that might be inaccurate or noisy, such as when a signal has a high amount of noise, the pattern is non-deterministic, or the point occurs on sharp rising or falling edges of a signal.
• Cycle Boundary — Indicates the cycle boundaries.
• VOH and VOL Levels — Indicates the V_OH and V_OL levels per pin.
• Driving — Indicates a driving pin state (0, 1, D).
• Not Driving — Indicates a non-drive pin state (L, H, X, V, M, E). An up or down arrow placed at the strobe time the time set specifies indicates the strobe edge of compare states.
• Unknown State — Indicates that sufficient drive state information does not exist for a particular section of the digital signal, such as before the Drive On edge at the beginning of a pattern, after a discontinuity, in situations where a dash (-) pin state cannot be resolved, or when information outside the pattern determines the drive state, such as a source waveform.

Configuring the Digital Scope

Use the Pattern, Pins/Pin Groups, and Site controls in the Digital Scope Configuration section to configure digital scope execution settings. Use the type-ahead drop-down menu to select valid pins and pin groups. Click the Enabled Sites button to launch the Sites dialog box, which you use to enable and disable sites defined in the active pin and channel map, typically for debugging purposes. Disabled sites do not return results. Use the Start Vector, Cycle Offset, Number of Cycles, Number of Steps, and Voltage Resolution controls in the Sweep Ranges section to configure sweep operation settings. The project stores the settings for the digital scope but not the plot data itself.

Note  

Setting the number of steps to a value that results in a resolution smaller than the timing accuracy the digital pattern instrument supports does not yield any additional improvements in the waveform accuracy.

Use the expander buttons to expand or collapse the settings section to create a larger display area for the digital scope.

When you right-click a cell in the pattern document and select Use Digital Scope on Selected Pins and Vectors from the context menu or right-click a cell in the History RAM View and select Use Digital Scope on Selected Pins and Cycles from the context menu, the digital scope preconfigures the Start Vector, Cycle Offset, Number of Cycles, Pins/Pin Groups, and Pattern settings for the digital scope operation based on the vector or cycle you selected.

You can also use the Site drop-down menu on the toolbar to select the site for which you want to display plot results.

While the digital scope is running, the vertical red points mark the point in time for which the levels on each pin are currently being evaluated. Green circles indicate fully evaluated points and always display while executing.

Configuring a small number of steps might result in incomplete waveform information if the signal changes rapidly.

Instrument settings restore to their original values when the digital scope operation completes or when you abort the operation.

Use the two cursors on the digital scope to display the timing and measured voltage values for all pins. You can drag the two cursors independently from each other to compute the time offset difference between the two locations and display the value in the top left corner of the digital scope. The cursors reset to the beginning of the digital scope plot when you restart the digital scope operation.

Use the Toggle Expected Waveforms on Top button to change whether the actual waveform overlays the expected waveform. Use the Always Show Sampled Points button to toggle the display of all points on the plot. The graph always displays the sampled points while executing. Use the Show Levels at Cursor button to toggle the display of the per pin voltage levels at the locations of the cursors.

Use the buttons above the digital scope to control panning and zooming. The pan and zoom locations reset to center when you restart the digital scope operation.

The document stores the specified digital scope settings, but not the graph data itself, in the corresponding .digiprojcache file for the project.

Note  

Once the Digital Pattern Editor calculates and applies TDR values, the Digital Scope's timing is now relative to the DUT. The time displayed in the Digital Scope represents the time the DUT drove or received the signal, not the time a digital pattern instrument drove or received the signal. Use the Digital Scope to validate signals driven from the DUT. The Digital Scope displays the expected waveform signals driven the DUT in blue.

Saving the Digital Scope Information

Use the Save Plot Data to CSV File button on the toolbar or <Ctrl+S> to save the actual and expected plot data for the active site to a .csv file. Use the Save Screenshot to PNG button on the toolbar to save a screenshot of the state and plot data of the digital scope as an image file. You must expand the settings section to include it in the image.

Keyboard Shortcuts within the Digital Scope