The following statements describe modeling combinatorial logic with the event control time control statement [@ (at)].
• A combinatorial always block has a sensitivity list appearing within parentheses after always@ .
• An always block is activated if an event (value change or edge) appears on one of the sensitivity list signals.
• The sensitivity list can contain:
° Any signal that appears in conditions, such as if or case.
° Any signal appearing on the right-hand side of an assignment.
• By substituting a * (asterisk) in the parentheses for a list of signals, the always block is activated for an event in any of the always block's signals as described.
• In combinatorial processes, if a signal is not explicitly assigned in all branches of if or case statements, Vivado synthesis generates a latch to hold the last value.
• The following statements are used in a process:
° variable and signal assignments
° if-else statements
° case statements
° for-while loop statements
° function and task calls