Question

I have a std_logic_vector and I need to know when some changes occur on it.
So far I wrote this:

process (cp, l1)
begin
    if rising_edge(cp) then
        rL1 <= l1;
    end if;
end process;
tickL1 <= rL1 xor l1;

rL1 is delayed version of l1, and l1 is the std_logic_vector I’m checking for changes. The problem is that xor returns std_logic_vector, but I need just 0 or 1. How can I get that?

Answer 1

You can use

change <= or_reduce(tickL1)

or

change <= or_reduce(rL1 xor l1);

Which OR’s all signals of the result together, so if any of these is 1 the signal change will also be 1.

Edit: All of these reduce functions are in ieee.std_logic_misc.all