• Hardware and software concepts
  • Hardware is part of the system design
  • Behavioral and RTL style
  • Structure
  • Concurrency (simultaneity)
  • Sequential statements
  • Description of timing behavior is possible
  • One language for model development and verification
  • VHDL extension towards analogue modeling with VHDL-AMS


Hardware and software concepts are present in VHDL to model a digital system. There is a clear distinction between a pure behavioral model and RT level modeling for synthesis.

VHDL permits a structural (modular) and hierarchical description of a digital system.

Concurrency is an important concept of VHDL: Concurrent statements are executed virtually in parallel. The simulation is event driven. If a certain event occurs (e.g. initiated by the stimulus), processes that depend on these events are triggered. These processes contain sequential statements which are evaluated one after another. Each process as a whole can be viewed as a concurrent statement. This way, the changes of signal values caused by the execution of several processes occur at the same time in the simulation.

Furthermore, it is possible to describe timing behavior in VHDL. This eliminates the need for other languages for stimuli generation for test purposes or timing verification of the final design.

Chapters of System Design > VHDL - Overview and Application Field