Encore SIM EDITOR SOFTWARE Guia do Utilizador descarregar pdf (Página 88)

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Modeling Your Design

@ (posedge clk) q <=d;

Even though clk is in an event control, it is not in the sensitivity

list event control.

• VCS does not infer the following latch to be a sequential device:

always begin

wait clk; q <= d; @ d;

end

There is no sensitivity list event control.

• VCS infers the following latch to be a sequential device:

always @ (clk or d)

if (clk) q <= d;

The sequential controls, clk and d, are in the sensitivity list event

control.

Avoid Level Sensitive Sensitivity Lists Whose Signals are Used

“Completely”

VCS infers a combinational device instead of a sequential device if

the following conditions are both met:

• The sensitivity list event control is level sensitive

A level sensitive event control does not contain the posedge or

negedge keywords.

• The signals in the sensitivity list event control are used

“completely” in the always block

Used “completely” means that there is a possible simulation event

if the signal has a true or a false (1 or 0) value.

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Encore SIM EDITOR SOFTWARE Guia do Utilizador Página 88