Talk:Sequential logic

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Although, for teaching reasons it would be grand to unite these two, quite often parallel, subjects into one article. Especially when there are state machines mentioned as a topic, which usually refer to simpler devices with more discrete states than "unpredictable" asynchronous designs. They look good under the same subject, and it could be implied that "these usually refer to 'synchronous design' although they also encompass asynchronous designs", which would be a link.

--Mikachu 12:34, 24 November 2006 (UTC)

Venjunction: undue

Not normally covered in mainstream sources on the topic of sequential logic (or logic design). Search google books or check one of the standard textbooks in the area. Tijfo098 (talk) 13:42, 9 April 2011 (UTC)

Request for major changes

• Change 1: I agree with Tijfo098 that "Venjunction" is undue. In fact, the three subsections named "Sequention", "Venjunctions", and "Realization" should be removed. These concepts may be interesting, but so far they have not been widely adopted by the community. A Google scholar search with these three terms only leads to 5 answers, all from the same author (V Vasyukevich). So, it is perhaps too early to have them adopted in Wikipedia. Anyway, this author has already a Wikipedia page Asynchronous_logic_(algebra) to expose his ideas.

• Change 2: The third section ("Clocked sequential system") is very weak and just duplicates or contradicts the remainder of the article, without paying attention to what has been said above. Also, there is a fundamental mistake in this section, as the author only considers that a sequential system is clocked (i.e., synchronous) without paying attention to the existence of asynchronous logics.

I suggest to remove this confusing section and dispatch some of its material in the previous sections. These are my comments on each sentence of this section.

 1) In digital electronics, a clocked sequential system is a system whose output depends only 
 on the current state, whose state changes only when a global clock signal changes, and 
 whose next-state depends only on the current state and the inputs.

This just duplicates the first paragraph of the article, but in a more restricted way as only clocked sequential "systems" are considered. The definition given in the first paragraph is more general and does not rely on the existence of a clock. So, this paragraph can be removed.

 2) Nearly all digital electronic devices (microprocessors, digital clocks, mobile phones, cordless 
 telephones, electronic calculators, etc.) are designed as clocked sequential systems. Notable 
 exceptions include digital asynchronous logic systems.
 3) In particular, nearly all computers are designed as clocked sequential systems. Notable exceptions 
 include analog computers and clockless CPUs.

The two next paragraph, which are very similar (!) have nothing to do with sequential logic. They just claim that synchronous circuits are more numerous than asynchronous circuits, which is globally correct, but irrelevant to the present Wikipedia article. To be accurate, an increasing number of synchronous circuits have asynchronous subparts, so the claims of these two paragraphs should be made more precise. Anyway, these two paragraphs can be removed too.

 4) Typically each bit of the "state" is contained in its own flip-flop. Combinational logic decodes 
 the state into the output signals. More combinational logic encodes the current state and the inputs 
 into the next-state signals. The next-state signals are latched into the flipflops under the control 
 of the global clock signal (a wire connected to every flip-flop).

This paragraph can be saved and moved in the section "Synchronous sequential logic".

 5) A clocked sequential system is a kind of Moore machine.

This is just said in the beginning of the article, so this loose statement should be removed.

More references needed

Altough I only studied part of the topic of asynchronous sequencial logic, I noted that several important works are not cited.

First of all, I support the fact that the references about venjuntions etc.. are quite controversial, not only because they are not in one single peer-reviewed publication, but also because those mathematical foundations have not shown yet practical implementations, mainly because it is not clear how to account for race conditions.

One of the main works in this area is D. A. Huffman, "The synthesis of sequential switching circuits"

Other important works are from S. Unger, and there is a nice review paper: D. B. Armstrong, A. D. Friedman, P. R. Menon, "Asynchronous design methodologies: an overview"

and I believe they should be cited — Preceding unsigned comment added by Sweetbomber (talk • contribs) 23:30, 28 July 2012 (UTC)