Specifications

Simulation Clearing and Initialization 75
 Any primitive type with storage capability (such as flip–flop, register,
or counter) that has a Don’t Know output value is cleared, either to its
specified initial value (if any) or to zero.
 A single device that currently has an unknown output state is randomly
selected and queued for re-evaluation. A special input mapping is done
so that all unknown inputs are treated as zero.
 The simulator is cycled repeatedly as long as the number of unknown
states in the design decreases.
 The last three steps are then repeated until the number of unknowns
ceases to diminish.
If this operation does not clear the design to an appropriate state, refer to
the other techniques discussed in following sections.
NOTE: Designs with “hard” unknowns, such as unconnected inputs or conflicting
outputs, will not be successfully cleared by this procedure. All device inputs
should be specified to a known value if not driven by other devices.
Setting Initial Values
You can specify initial values for signals and pins. These values will be
applied by the Clear Simulation and Clear Unknowns operations, as
described in the preceding sections.
For both object types, the initial value is entered into an attribute field,
either Initial.Sig or Initial.Pin. The allowable values consist of a single
character chosen from the following table.
All other values will be ignored.
Character Value
0LOW
1HIGH
Z HIGHZ
X DONT01
LW Reference.bk Page 75 Monday, December 15, 2003 5:59 PM