Event Control Time Control Statement - 2023.2 English

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