Latches, Flip-Flops and Registers
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Finally, when considering the use of transitions between ‘0’ and
‘1’, there are issues with synthesis and simulation when using the
different approaches. For example, with the standard logic package
(std_logic variables), the transitions are strictly defined and so we
may have the case of high impedance or don’t care states occurring
during a transition. This is where the rising_edge (and its opposite
the falling_edge) function are useful as they simplify all these
options into a single function that handles all the possible transi-
tion states cleanly.
It is generally best, therefore, to use the rising_edge or falling_ ...