Adiabatic circuit

Adiabatic circuits are low power circuits which use "reversible logic" to conserve energy.Unlike traditional CMOS circuits, which dissipate energy during switching, adiabatic circuits attempt to conserve charge by following two key rules:   
1. Never turn on a transistor when there is a voltage potential between the source and drain.
2. Never turn off a transistor when current is flowing through it. Read more



social network | email spam | customer retention | text in email | email marketing best practices

Reversible Process (Thermodynamics)

In thermodynamics, a reversible process, or reversible cycle if the process is cyclic, is a process that can be "reversed" by means of infinitesimal changes in some property of the system without entropy production or dissipation of energy. Due to these infinitesimal changes, the system is in thermodynamic equilibrium throughout the entire process. Continue Reading

Biiliard-ball computer

A billiard-ball computer, also known as a conservative logic circuit, is an idealized model of a reversible mechanical computer based on newtonian dynamics, proposed in 1982 by Edward Fredkin and Tommaso Toffoli. Instead of using electronic signals like a conventional computer, it relies on the motion of spherical billiard balls in a friction-free environment made of buffers against which the balls bounce perfectly. It was devised to investigate the relation between computation and reversible processes in physics. Continue Reading

Three-input universal logic gate

Logic gates are used to build computer chips. Reversible logic gates are of interest because they could in principle generate useful results for less heat generated (Landauer 1961). The nand gate is universal among irreversible logic gates, in the sense that it is possible to simulate any irreversible logic gate with a network of these gates. The Fredkin and Toffoli gates were the first gates to be proved universal among reversible logic gates. Read more

Reversible Cellular Automaton

A reversible cellular automaton is a cellular automaton in which every configuration has a unique predecessor. That is, it consists of a regular grid of cells, each of which may take on one of a finite set of states, together with a rule for updating all cells simultaneously based on the states of the neighboring cells, in such a way that the state of each cell prior to an update can be determined uniquely from the updated states of all the cells. The time-reversed dynamics of a reversible cellular automaton can always be described by another cellular automaton rule, possibly on a much larger neighborhood. Read more

Reversible circuits

To implement reversible computation, estimate its cost, and to judge its limits, it is formalized it in terms of gate-level circuits. For example, the inverter (logic gate) (NOT) gate is reversible because it can be undone. The exclusive or (XOR) gate is irreversible because its inputs cannot be unambiguously reconstructed from an output value. However, a reversible version of the XOR gate --- the Controlled NOT gate(CNOT) --- can be defined by preserving one of the inputs. Read more

Three-input universal logic gate

Logic gates are used to build computer chips. Reversible logic gates are of interest because they could in principle generate useful results for less heat generated (Landauer 1961). The nand gate is universal among irreversible logic gates, in the sense that it is possible to simulate any irreversible logic gate with a network of these gates. The Fredkin and Toffoli gates were the first gates to be proved universal among reversible logic gates. Read more

Reversible dynamics

In mathematics, a dynamical system is invertible if the forward evolution is one-to-one, not many-to-one; so that for every state there exists a well-defined reverse-time evolution operator. Read more

Fredkin gate

The Fredkin gate (also CSWAP gate) is a computational circuit suitable for reversible computing, invented by Ed Fredkin. It is universal, which means that any logical or arithmetic operation can be constructed entirely of Fredkin gates. The Fredkin gate is the three-bit gate that swaps the last two bits if the first bit is 1. Read more

Toffoli gate

In computer science, the Toffoli gate (also CCNOT gate), invented by Tommaso Toffoli, is a universal reversible logic gate, which means that any reversible circuit can be constructed from Toffoli gates. It is also known as the "controlled-controlled-not" gate, which describes its action. Read more

Reversible computing

Reversible computing is a model of computing where the computational process to some extent is reversible, i.e., time-invertible. A necessary condition for reversibility of a computational model is that the relation of the mapping states of transition functions to their successors should at all times be one-to-one. Reversible computing is generally considered an unconventional form of computing. Read more

Reversible design of Two pair Two rail checker:

The two pair two rail checker is required for testing that the outputs in CTSG blocks are complementary or not. Thus the efficient reversible design of two pair two rail checker is discussed in this section. The error checking functions required in the two pair rail checker are as follows
                                                                         E1=x0y1+y0x1
                                                                         E2= x0x1+y0y1
                                                     Where x0/y0 & x1/y1 are complementary,
The two pair rail checker produces the complementary output at E1& E2, if the inputs passed to it are complementary. If the inputs are not complementary, the outputs E1 & E2 will be identical

Verilog digital logic simulator tools allow you to perform the following tasks in the design process without building a hardware prototype:

1. Determine the feasibility of new design ideas
2. Try more than one approach to a design problem
3. Verify functionality
4. Identify design problems.

Overview Of Reversible Logic Synthesis Methods

1.  Composition methods:
The idea is to compose a reversible block using small and well known reversible gates. The reversible block should be easy to use. Then, a modification of a conventional logic synthesis procedure is applied to synthesize a network. The resulting network will be reversible as a network essentially consisting of reversible gates.

2.  Decomposition methods:
 Decomposition methods can be characterized as a top down reduction of the function from its outputs to its inputs. During the design procedure a function is supposed to be decomposed into a combination of several specific functions each of which is realized as a separate reversible network .An example of a decomposition method can be found in where synthesis appears to be a reduction of the output to the form of the input. The decomposition and composition methods can be multilevel. Observe that the composition and decomposition methods form a very general and powerful tool of logic synthesis. In fact, most of the algorithms can be classified as either composition or decomposition. Using Lemma 1, one can notice the duality of the composition and decomposition methods; a composition design procedure for a reversible function f is a decomposition procedure for fi1.

Advantages of storing the Intermediate results

The achievements obtained using this method is:

1. No erasing of bits is done as in the irreversible process.
2. Heat dissipation is not there as the bits are not erased and hence power is saved.
3. And the inputs can be obtained from the outputs.

      

Main reasons of Important role of HDL in mordern design methodology

Design functionality can be verified early in the design process. Design simulation at this higher level, before implementation at the gate level, allows you to evaluate architectural and design decisions. Coupling HDL Compiler with logic synthesis tools, you can automatically convert an HDL description to a gate-level implementation in a target technology.HDL descriptions provide technology independent documentation of a design and its functionality. Since the initial HDL design description is technology-independent, you can use it again to generate the design in a different technology, without having to translate from the original technology.

Procedure vs Continuos assignment statement

Procedural assignment changes the state of a register

  sequential logic

  Clock controlled

Continuous statement is used to model combinational logic. Continuous assignments drive wire variables and are evaluated and updated whenever an input operand changes value. It is important to understand and remember the difference.

Tasks and Functions

Tasks are like procedures in other programming languages, e. g., may have zero or more arguments and do not return a value. Functions act like function subprograms in other languages. Except A Verilog function must execute during one simulation time unit. That is, no time controlling statements, i. e., no delay control (#), event control (@) or wait statements, allowed. A task may contain controlled statements. A Verilog function cannot invoke (call, enable) a task; whereas task may call other tasks and functions.

Lexical convections

Verilog is a free-format language like c-language.

2. White space can be used freely

3. Verilog is a case-sensitive language.

4. User provided names for the verilog objects in the descriptions.

5. Legal characters are “a-z”, “A-Z”, “0-9”,   “_”, and “$”.

6. First character has to be a letter or an “_”.

7. Example: Count,  _R2D2, Fives$

8. Predefined identifiers to define the language constructs.

9. All keywords are defined in the lower case cannot be used as identifiers.

10. Example: initial, assign, module