vhdl D-Flip-Flops (DFF) and latches


D-Flip-Flops (DFF) and latches are memory elements. A DFF samples its input on one or the other edge of its clock (not both) while a latch is transparent on one level of its enable and memorizing on the other. The following figure illustrates the difference:

DFF vs. latches behavior

Modelling DFFs or latches in VHDL is easy but there are a few important aspects that must be taken into account:

  • The differences between VHDL models of DFFs and latches.

  • How to describe the edges of a signal.

  • How to describe synchronous or asynchronous set or resets.