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VHDL (VHSIC-HDL, Very High-Speed Integrated Circuit Hardware Description Language) is a hardware description language used in electronic des...

Tuesday 13 October 2009

Digital Design

As i have mentioned earlier that digital design concepts has to be crystal clear while you design a digital circuit. Here we will stat with the basic concepts of digital designing.

Digital or binary logic has fascinated many people over the years. The very idea that a two-valued number system can possibly be the basis for the most powerful and sophisticated computers seems astounding, to say the least. Nevertheless, it is so, and the how and the why of this requires some explanation.

Everything in the digital world is based on the binary number system. Numerically, this involves only two symbols: 0 and 1. Logically, we can use these symbols or we can equate them with others according to the needs of the moment. Thus, when dealing with digital logic, we can specify that:

0 = false = no
1 = true = yes

Using this two-valued logic system, every statement or condition must be either "true" or "false;" it cannot be partly true and partly false. While this approach may seem limited, it actually works quite nicely, and can be expanded to express very complex relationships and interactions among any number of individual conditions.

Digital logic may be divided into two classes:

=> combinational logic, in which the logical outputs are determined by the logical function being performed and the logical input states at that particular moment. A simple combinational circuit is shown below.

=>sequential logic, in which the outputs also depend on the prior states of those outputs. Both classes of logic are used extensively in all digital computers. A Latch is considered to be a simplest sequential circuit. A simple sequential circuit is shown below.

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