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Question about VCD content

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ruwan2

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Hello,

I wrote some Verilog code a long time ago. Now I get some VCD code as below. I find some lines cannot be understood, such as: 

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$dumpvars
xaaaaa
xaaaab
xaaaac
xaaaad
$end
 
 
#1
1aaaaa



I guess that the above question could be resulted from below:

$var wire 1 aaaaa A $end

Does it say a 5-bit signal?
'x' at the beginning means undetermined value?

Can you explain it to me above?

Thanks,



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$date
     Dec 24, 2016       16:54:43
$end
 
$version
 SystemC 2.3.1-Accellera --- Dec 22 2016 15:46:30
$end
 
$timescale
     1 ps
$end
 
$scope module SystemC $end
$var wire    1  aaaaa  A       $end
$var wire    1  aaaab  B       $end
$var wire    1  aaaac  C       $end
$var wire    1  aaaad  D       $end
$upscope $end
$enddefinitions  $end
 
$comment
All initial values are dumped below at time 0 sec = 0 timescale units.
$end
 
$dumpvars
xaaaaa
xaaaab
xaaaac
xaaaad
$end
 
#0
0aaaaa
1aaaab
0aaaac
1aaaad
 
#1
1aaaaa
 
#2
0aaaaa
0aaaab
1aaaac
0aaaad
 
#3
1aaaaa
 
Last edited by a moderator:

The format of VCD files is explained in section 21.7 of the
Code: 
$var [ var_type size identifier_code reference ] $end
So you have a wire, that is 1-bit, using the reference code aaaaa, for the signal A.
xaaaaa means the signal A has the value x
 

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