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A VCD is an ascii file (that's both an advantage and disadvantage) describing a digital waveform from a VHDL/Verilog simulator.
First there is a header describing the names of the signals in the file, followed by an abbreviation code (1 character) that will be used everywhere later on to refer to the signal (to save space in the file)
In the remainder of the file it contains 1 time instant per line of text, and only the changing signals that occur at that time point. (hence the name CHANGE dump).
Modelsim .wlf files are much more flexible, though, and they can also be manipulated programmatically.
VCD or Value Change Dump. This particular format is used inorder to capture the signal transitions. We can use $dumpvars in verilog which will dump all the signals in the specified VCD file. The need to have a VCD file is that we can take this as input to any of the waveform viewer like signal scan, Debussy expects FSDB format.
when you debug you functionality, you should choose fsdb. but when you still consider power analysis, you should choose VCD. however, VCD file is two large.
If you are using Signalscan to watch the waveform, VCD file is huge not convenient at all--each time you have to convert a VCD file to db file. Try to use "simulation history manager" instead of VCD, which is much more favorable.
U can get the VCD after simulation. If u feel it is big, convert it to fsdb using vfast which is provided by Novas. So now u can use VCD and fsdb, but using the converted fsdb from VCD does not supports some major features of nWave(Novas)
VCD-Value Change Dump. This format is used to capture the signal transitions. We can use $dumpvars in verilog which will dump all the signals in the specified VCD file. The need to have a VCD file is that we can take this as input to any of the waveform viewer like signal scan, Debussy expects FSDB format.
gold_kiss above has already answered almost by the same words.
Warning!
vcd really is huge. If you use vcs tools, you can use vpd file instead of vcd file and the vpd file is very small because of its binary file. You can watch the waveform by opening the vpd file. Additionally if you really want to use the vcd file, you can get it from the vpd file by the synopsys command "vpd2vcd".
VCD is a standard format for many different tools, for ATE and power analysis, fsdb is novas format and is small size. but I think all these are accepted by popular EDA tools.
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