a. Import Acquired or Simulated Test Vectors
The NI Digital Waveform Editor can open Hierarchical Waveform Storage (HWS), ASCII, and VCD files. The HWS file format is an open standard used for storing scientific and engineering data. It is capable of saving device configuration settings as well as multiple channels of waveform data, measurements, and associated header information. HWS also offers compression options, making this format the best choice for very large or multiple data records.
Although not as flexible, ASCII files and Value Change Dump (VCD) files are also commonly used to store digital data, especially from many simulation and design packages. ASCII files represent standard text files that can be opened by all common spreadsheet and word processing applications. VCD files are based on the IEEE 1364-2001 standard and are the common file format used to save data from industry-standard Electronic Design Automation (EDA) computer-aided design (CAD) tools.
Opening an HWS file
To open an HWS file, such as one saved from an acquisition program in SignalExpress, select
File » Open Waveform… to open a dialog box where you can select the desired waveform file. Navigate to an HWS file and click “open.”
Importing an ASCII file
To import an ASCII file, select
File » Import » From ASCII... to launch the ASCII Import Wizard. Follow the instructions in the wizard to select the source file, data representation, column delimiters, start row and start column, and the number of columns and rows to import. You can also specify whether the first row is imported as the signal names, which appear to the left of the data on the waveform graph. Use the Data Preview portion of the dialog box to verify that the selected settings will import the desired data from the ASCII file.
Importing a VCD file
To import a VCD file, select
File » Import » From VCD... to launch the VCD Import Wizard. The VCD Import Wizard guides you through a three-step process for selecting the signals to import, configuring a sampling method, and identifying whether the signal is drive or compare data. The first step allows you to select the VCD file, to configure options for importing data, and to view information about the data. The second step allows you select a sampling method for the signals in the VCD file. Your choice of sampling method specifies how the Import Wizard converts the asynchronous VCD file into a synchronous, discrete set of test patterns. In the third and final step of the wizard, you configure how the X (don't care) and Z (tristate) states are imported.
Most logic analyzers include cursors, a vertical line indicating a specific time or sample number across all of the channels on the waveform graph, to allow you to quickly view the timing relationships between the rising and falling edges of all the channels. Multiple cursors provide the ability to measure the time delta between edges of the same channel.
The NI Digital Waveform Editor has two cursors that can help in analyzing the timing relationships. To enable the cursors, navigate to
View » Show Cursors. You can then use the cursors to measure the distance between two edges on a digital signal. Use the mouse to drag the cursors across your digital signals. The Cursor Delta, shown in the status bar at the bottom of the waveform graph, displays the difference in samples and time of where the two cursors are positioned.
c. Zoom Tools
In order to quickly determine whether your digital system produced the correct results or not, you need to be able to change the zoom of the displayed data. With the NI Digital Waveform Editor, you can adjust the number of waveform samples displayed by using four different zoom tools. These tools allow you to easily switch from viewing your digital data in its entirety to analyzing a specific number of samples. The four zoom tool icons are shown below with a brief description of their functionality.
- Zoom In - Use the Zoom In tool to change the number of samples visible in the waveform graph to half the current number of samples. The sample in the far left location on the waveform graph remains the same.
- Zoom Out - Use the Zoom Out tool to change the number of samples in the waveform graph to twice the current amount. The sample in the far left location on the waveform graph remains the same, except when the end of the waveform is reached, in which case the left sample viewed is adjusted to accommodate the desired number of samples.
- Zoom to Selection - Use the Zoom To Selection tool to cause the currently highlighted samples to fit within the viewing area. If the highlighted area is smaller than the viewing size, the Zoom To Selection tool places the leftmost sample of the highlighted area on the left of the graph and zooms only to the minimum viewing size. (NOTE: This option is only available when a portion of the waveform is highlighted.)
- Show Entire Waveform - Use the Show Entire Waveform tool to zoom in or out to place the entire waveform in the waveform graph.
A bookmark is a way to mark a section of a digital waveform so that it can easily be found at a later time. You can use bookmarks when dealing with large waveforms and you need to be able to return to areas of interest after looking through the rest of the waveform. To add a bookmark to a digital waveform, right-click on the area of interest and choose the
option. This opens a dialog box where the name and exact position, in samples, of the bookmark can be specified.
To return to a previously created bookmark, right click on the display, choose
and specify the bookmark you wish to view.
e. Search for Pattern
The final feature that is critical in expediting the debugging of your digital system is the ability to search for a specific, known pattern buried somewhere in all of the acquired data. To search for a specific pattern in a digital waveform, select
Edit » Find… to open a dialog box where custom patterns can be entered. Enter the pattern you wish to search for by typing either a “0”, “1”, “Z”, “H”, “L”, or “X” in successive data positions on the channel(s) you wish to search.
Search button to locate the first instance of the custom pattern in the currently loaded waveform. To find the next instance of this pattern, click the
Find Next button.