VCD Files

Signal data can be imported into the ChronoVu viewer from an IEEE standard VCD (Value Change Dump) file. The VCD file format is an ASCII text format for waveform information, which can be generated by many popular logic simulators, logic analyzers, and waveform viewers. The VCD file import function provides an easy method for comparing the results from two or more ChronoVu acquisitions or for comparing simulated results to acquired results.

Importing the Data

To import the data from a VCD file, click on the File–>Import Data from a VCD file menu item from the menu bar. (see User Interface for assistance). Once a VCD file is selected for importation, the VCD Signal Import pop-up window (shown below) will be displayed. Select the signal to be imported, and the ChronoVu channel into which the data is to be imported, on the menu. The imported signal can be adjusted to the desired position on the time axis by entering appropriate values in the alignment section of the menu. If you are not sure how the signals should be aligned, simply import the signal using zeros in the alignment fields. Once the signal has been imported, use the markers (left and right mouse buttons) to locate the points in the data that should be aligned. The signal can then be imported again (into the same ChronoVu channel) entering the pointer locations (displayed in the user hints area) to realign the data as needed.

Notes Regarding Imported VCD Waveform Data

Because ChronoVu channels are designed to display one-bit acquired data, they can only display signals specified in the VCD file as type “wire” or type “reg”, and having a width of 1 bit. Signals that can not be displayed will not appear in the signal selection section of the VCD Signal Import menu. During any periods when the imported signal values are specified as “x” (unspecified) or “z” (high impedance) the ChronoVu software will display the imported signal as unchanged from its last valid (one or zero) state. At points along the time axis that proceed the imported data, the displayed state will be that specified in the $dumpvars (initial condition) section of the VCD file. A value of zero will be used if no $dumpvars section is available. At points along the time axis that follow the last data transition in the VCD file the displayed data will remain static.

Other VCD File Import Limitations

For ChronoVu signal import, lines in the VCD file must not exceed 120 characters. Signal names may be up to 120 characters, but must not contain spaces or other white space characters. VCD signal identifiers will be truncated to the first 10 characters if they exceed 10 characters in length. In order to keep the signal name length brief, the text specified in the $scope section of the VCD file is not prepended to the signal names displayed in the VCD Signal Import menu, thus signals with the same name but different scope will be displayed as similar names on the menu. Once a signal is imported, the signal name will be truncated to the rightmost 12 characters for display in the ChronoVu signal name window.