(Compare) 9: Mask Sections to Exclude Comparison

It is sometimes useful to mask some segments during comparison. In this example, we will create a Compare_Enable signal that will specify the specific clock segments over which we want the comparison to be performed. Then we will use a Boolean equation (Offset_Clock and Compare_Enable) in a simulated signal to define the region in which to perform the compare. Since this step uses simulated signals you will need to be using a product that supports this feature like WaveFormer Pro (not one of the Viewers).

Search and Replace Signal Names:

First, we will change the names of the signals in the diagram so that when we add the simulated signal, we do not get simulation errors (with the signal names Test.* the simulator will look for a module that we will not have defined).

•Press <CTRL>A to select all of the signals in the diagram. The Search and Rename signals feature will search the selected signals. If no signals are selected, then a dialog will appear asking if you would like to select all signals in the diagram.

•Select the Edit > Search and Rename Signals menu option to open the Search and Rename Signals dialog.

•Enter Test. in the Old Name edit box.

•Enter Test_ in the Signal Name Replacement edit box.

•Click OK to close the dialog and rename the signals.

searchAndReplaceSignalNamesDialog

Add the Compare Enable Signal:

•Add a new signal called Compare_Enable and draw the following waveform that is high between 4ns and 8ns

mask_ck_enable_wfm

Add the Simulated Masking Signal

Next, place a simulated signal in the diagram to use as the clocking signal for the comparison:

•Add a signal to the diagram and set the following properties in the Signal Properties dialog:

•Set the Name to Masking_Signal.

•Select the Simulate radio button (instead of Drive).

•Enter Offset_Clock and Compare_Enable in the Boolean Equation edit box.

maskingSignalProperties

•Press the Simulate Once button to generate the simulated signal.

mask_ck_simulate_sig

•Notice that the masking signal is high only during the times that both the Compare_Enable and the Offset_Clock are high. These are the clock segments that are not masked. The comparison will be performed during these segments.

Use the Masking Signal to Mask Clock Segments

Next we will edit the compare signals so that they use the new Masking_Signal as a clock.

•Either press the SET ALL button or choose the View > Compare and Merge > Edit Compare Signals menu to select all the compare signals and open the Signal Properties dialog.

•Set the Clock to Masking_Signal.

•Click Compare to apply the changes and perform the comparison.

mask_sig_proper_compare

diagramComparison_masked

•Notice that the first and last differences that were previously in the diagram have now disappeared, because they are masked from the comparison.