Working with VCD Files

Its very convenient to take simulation waveform diagrams and convert them to a timing diagram. If you create a VCD file while running simulations, just open the VCD file as you would a timing diagram file. The program will read and parse VCD file and convert it to a timing diagram automatically and save it in the same directory the VCD file is in.


Use File→open from the menu or toolbar button, and select *.vcd in the file filter in the dialog. Select the VCD file. The TimingAnalyzer reads the VCD file and automatically converts it to a timing diagram that is saved in the same directory the VCD file is in.


This option will be added. Saving diagrams as VCD files can be useful for simulation test vectors.

Bus Signals

Some VCD files don’t seem to contain buses so there a function, “Bus Signals” that can be used to make buses from sequentially ordered signals like ADIO<31>, ADIO<30>, ADIO<29> …

If you want to bus signals, select the signals, click the right mouse button to bring up the pop-up menu, and select “Bus Signals”. The new bus should appear above the most significant signal in the diagram.


VCD files are commonly very large files when produced from simulators. The TimingAnalyzer does not handle large files very well at this time because it was original designed to work with small text timing diagram files, so I limited the file size to 100,000 lines. This is hardcoded in the VCD parser, so the first 100,000 lines of any VCD will be parsed and displayed. It is recommended to create smaller sized VCD files from simulations that contain just the transactions of interest that you want to convert to a timing diagram.

It is possible to run out of memory on the heap if there are lots of edges in the vcd file. If this happens, a java “OutOfMemory” error occurs. you can increase the memory limit allocated for the program by running the program from the command line as shown below

java -Xmx512m -jar TimingAnalyzer.jar

-Xmx512m specifies the maximum heap memory the program can use in MBytes, in this case 512M Bytes

User Support

Beta 0.947 is the first release with this feature. If you find a VCD file that is not loading properly, please send me a copy and I will do my best to fix asap.


  1. VCD $dumpvars is supported but not $dumpports. $dumpports includes port driver data and is used typically used to drive a tester.
  2. The first 100,000 lines of a VCD file are parsed and converted to a timing diagram. All lines after are ignored.
  3. If signal definitions take more than 100,000 lines, the VCD file will cause an “OutOfBounds” Exception. Close the empty tab window.

Testing ( Request for VCD example files )

  1. All VCD files tested use binary notations for signal values changes. Can anyone provide example VCD files that use hex notations for bus signals?
  2. Scopes are added to the signal names to keep hierarchy information. Can anyone provide example VCD files that contain signal names with hierarchy?