Priority Encoder

An encoder essentially performs the reverse of a decoder function in a combinational logic circuit. The process of converting from symbols or numbers to coded format is called encoding. A priority encoder has a priority function which allows it to produce an output corresponding to the highest-order input.

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Seven-Segment Display

Seven-Segment displays (7sd) are typically used in watches, calculators, and instruments to display decimal data. By lighting up a specified pattern of 7 LEDs, this type of decoder can create numbers 0-9 for digital display.

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A shifter is a circuit that produces an N-bit output based on an N-bit data input and an M-bit control input, where the N output bits are place-shifted copies of the input bits, shifted some number of bits to the left or right as determined by the control inputs.

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Delay of Combinational Circuits

Propagation Delays

Time is required to process information in digital circuits. This processing time is divided between the less significant signal transmission time, and the more significant propagation delays associated with switching logic circuits. If not managed properly, propagation delays can result in logic circuits that run too slowly to meet their requirements, or that fail altogether.

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Propagation delays not only limit the speed at which a circuit can operate, they can also cause unexpected and unwanted transitions in outputs. These unwanted transitions, called “glitches”, result when an input signal changes state, provided the signal takes two or more paths through a circuit and one path has a longer delay than the other.

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Bit-Slice Design Approach

When designing circuits with bussed inputs that represent binary numbers, it is often easier to consider a circuit designed for a single pair of bits, rather than for the entire binary number. This method of analysis is called Bit-Slice.

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Ripple Carry Adder (RCA)

Adder circuits add two N-bit operands to produce an N-bit result and a carry out signal (the carry out is a '1' only when the addition result requires more than N bits).

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Negative Binary Numbers

Signed Magnitude and 2's Compliment

Digital circuits that perform arithmetic functions often must deal with negative numbers, so a method of representing negative numbers must be defined.

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Ripple Borrow Subtractor

Subtracting circuits use two N-bit operands to produce an N-bit result and a borrow out signal.

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Hardware Multipliers

Hardware multipliers, based directly on adder architectures, have become indispensable in modern computers.

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Arithmetic and Logic Units (ALU)

Arithmetic and Logic Units (or ALUs) are found at the core of microprocessors, where they implement the arithmetic and logic functions offered by the processor (e.g., addition, subtraction, AND'ing two values, etc.). An ALU is a combinational circuit that combines many common logic circuits in one block.

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Introduction to Memory Circuits

Memory circuits function by storing the voltage present on an input signal whenever they are triggered by a control signal. They retain that stored voltage until the next assertion of the control (or trigger) signal. Between assertions of the control signal, the input signal is ignored and the output is driven to the most recently stored voltage.

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SR-Latch, D-Latch

A latch is one of the basic memory elements that store information in a digital system. One latch can store 1-bit of information. The outputs of a latch are constantly changing according to the inputs as long as the latch is enabled.

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Flip-Flop circuits are constructed in such a way as to make them operate properly when they are part of a sequential circuit that employs a single clock.

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Introduction to State Machines

Although combinational logic circuits form the backbone of digital circuits, sequential circuits are used in the vast majority of useful devices; there are more than 100 billion in existence.

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Design Sequential Circuits

The most difficult task in designing sequential circuits occurs at the very start of the design; in determining what characteristics of a given problem require sequential operations, and more particularly, what behaviors must be represented by a unique state.

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Structural Implementation of State Diagram

A state diagram with state codes and complete branching conditions contains all information required for the design of optimal next-state and output logic circuits.

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Introduction to Circuits

Electric Vs. Electronic, Analog Vs. Digital

A collection of electronic components that have been assembled and interconnected to perform a given function is commonly referred to as a circuit. Electronic circuits can be divided into two broad categories: digital and analog.

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Physical Circuits Vs. Model Circuits

Physical circuits are constructed of real, physical devices. Physical circuits can be inspected, tested, and modified. They consume electric power when energized, and they can function properly and do some meaningful work, or they can malfunction and create serious hazards to health and property. Model circuits are built on a computer and simulate the workings of the circuit, which allows for testing before the physical circuit is created.

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Electronic Components

Devices that Allow a Circuit to Function Properly

Resistors are two-terminal devices that restrict, or resist, the flow of current. The larger the resistor, the less current can flow through it for a given voltage as demonstrated by Ohm's law. Electrons flowing through a resistor collide with material in the resistor body, and it is these collisions that cause electrical resistance.

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Basic Digital I/O

Slide Switch, Push Button, and LED

Circuits often require inputs that come directly from users (as opposed to inputs that come from other devices). User-input devices can take many forms, among them keyboards (as on a PC), buttons (as on a calculator or telephone), rotary dials, switches and levers, etc.

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Printed Circuit Boards

The Base for Electrical Components

Electronic components are often assembled and interconnected on a flat surface known as a circuit board. The several types of existing circuit boards may be divided into two broad categories: those intended for prototype or experimental circuits, and those intended for production and/or commercial sale.

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Translating Information to and From Your Board

The Digilent® boards use several connectors for various purposes, but in general, they all communicate electronic information between the board and outside devices. By convention, connectors are given the reference designator “J__”.

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Integrated Circuits

A collection of one or more gates fabricated on a single silicone chip is called an integrated circuit. Here we will discuss the elements of an integrated circuit and how those element function.

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