ModelSim VCD commands and VCD tasks

ModelSim VCD commands map to IEEE Std 1364 VCD system tasks and appear in the VCD file along with the results of those commands. The table below maps the VCD commands to their associated tasks.

VCD commands	VCD system tasks
vcd add	$dumpvars
vcd checkpoint	$dumpall
vcd file	$dumpfile
vcd flush	$dumpflush
vcd limit	$dumplimit
vcd off	$dumpoff
vcd on	$dumpon

ModelSim versions 5.5 and later also support extended VCD (dumpports system tasks). The table below maps the VCD dumpports commands to their associated tasks.

VCD dumpports commands	VCD system tasks
vcd dumpports	$dumpports
vcd dumpportsall	$dumpportsall
vcd dumpportsflush	$dumpportsflush
vcd dumpportslimit	$dumpportslimit
vcd dumpportsoff	$dumpportsoff
vcd dumpportson	$dumpportson

ModelSim versions 5.5 and later support multiple VCD files. This functionality is an extension of the IEEE Std 1364 specification. The tasks behave the same as the IEEE equivalent tasks such as $dumpfile, $dumpvar, etc. The difference is that $fdumpfile can be called multiple times to create more than one VCD file, and the remaining tasks require a filename argument to associate their actions with a specific file.

VCD commands	VCD system tasks
vcd add -file <filename>	$fdumpvars
vcd checkpoint <filename>	$fdumpall
vcd files <filename>	$fdumpfile
vcd flush <filename>	$fdumpflush
vcd limit <filename>	$fdumplimit
vcd off <filename>	$fdumpoff
vcd on <filename>	$fdumpon

Important: Note that two commands (vcd file and vcd files) are available to specify a filename and state mapping for a VCD file. Vcd file allows for only one VCD file and exists for backwards compatibility with ModelSim versions prior to 5.5. Vcd files allows for creation of multiple VCD files and is the preferred command to use in ModelSim versions 5.5 and later.

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