Example VCD File
$date Date text. For example: November 11, 2009.
$end
$version VCD generator tool version info text.
$end
$comment Any comment text.
$end
$timescale 1ps $end
$scope module logic $end
$var wire 8 # data $end
$var wire 1 $ data_valid $end
$var wire 1 % en $end
$var wire 1 & rx_en $end
$var wire 1 ' tx_en $end
$var wire 1 ( empty $end
$var wire 1 ) underrun $end
$upscope $end
$enddefinitions $end
$dumpvars
bxxxxxxxx #
x$
0%
x&
x'
1(
0)
$end
#0
b10000001 #
0$
1%
0&
1'
0(
0)
#2211
0'
#2296
b0 #
1$
#2302
0$
#2303
The code above defines 7 signals by using $var:
$var type bitwidth id name
The id is used later on the value change dump. The value change dump starts after $enddefinitions $end and is based on timestamps. Timestamp is denoted as '#' followed by number. On each timestamp the list of signals that change their value is listed. This is done by the value/id pair:
new_value id
Read more about this topic: Value Change Dump
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