Encore SIM EDITOR SOFTWARE Guida Utente Scaricare il pdf (Pagina 89)

2-21

Modeling Your Design

The following code examples illustrate this rule:

Example 1

VCS infers that the following always block is combinatorial, not

sequential:

always @ (a or b)

y = a or b

Here the sensitivity list event control is level sensitive and VCS

assigns a value to y whether a or b are true or false.

Example 2

VCS also infers that the following always block is combinatorial, not

sequential:

always @ (sel or a or b)

if (sel)

y=a;

else

y=b;

Here the sensitivity list event control is also level sensitive and VCS

assigns a value to y whether a, b, or sel are true or false. Note that

the if-else conditional statement uses signal sel completely, VCS

executes an assignment statement whether sel is true or false.

Example 3

VCS infers that the following always block is sequential:

always @ (sel or a or b)

if (sel)

y=a;

Here there is no simulation event when signal sel is false (0).

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Encore SIM EDITOR SOFTWARE Guida Utente Pagina 89