Technical data

ModelSim VCD commands and VCD tasks
492
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Value Change Dump (VCD) Files ModelSim EE/PLUS Reference Manual
Model
Sim
VCD commands and VCD tasks
Model
Sim
VCD commands map to IEEE 1364 VCD system tasks and appear in
the VCD file along with the results of those commands. The table below shows
the mapping of the extended VCD commands to the IEEE 1364 keywords.
In addition to the commands above, the
vcd comment
command (p381) can be
used to add comments to the VCD file.
Resimulating a VHDL design from a VCD file
A VCD file intended for resimulation is created by capturing the ports of a VHDL
design unit instance within a testbench or design. The following discussion shows
you how to prepare a VCD file for resimulation. Note that the preparation varies
depending on your design.
Extractin
g
the proper stimulus for bidirectional ports
To extract the proper stimulus for bidirectional ports, the
splitio
command (p369)
must be used before creating the VCD file. This splits bidirectional ports into
separate signals that mirror the output driving contributions of their related ports.
By recording in the VCD file both the resolved value of a bidirectional port and
its output driving contribution, an appropriate stimulus can be derived by
-
vcdread
. The
splitio
command (p369) operates on a bidirectional port and creates
a new signal having the same name as the port suffixed with "__o". This new
VCD commands VCD s
y
stem tasks
vcd add
(p379) $dumpvars
vcd checkpoint
(p380) $dumpall
vcd file
(p382) $dumpfile
vcd flush
(p384) $dumpflush
vcd limit
(p385) $dumplimit
vcd off
(p386) $dumpoff
vcd on
(p387) $dumpon