From Digital Principles & Logic Design

So far, all of the logic circuits we have studied were basically based on the analysis and design of combinational digital circuits. Though these type of circuits are very important, they constitute only a part of digital systems. The other major aspect of a digital system is the analysis and design of sequential digital circuits. However, sequential circuit design depends, greatly, on the combinational circuit design.

The logic circuits whose outputs at any instant of time depend only on the input signals present at that time are known as combinational circuits. The output in combinational circuits does not depend upon any past inputs or outputs. Moreover, in a combinational circuit, the output appears immediately for a change in input, except for the propagation delay through circuit gates.

On the other hand, the logic circuits whose outputs at any instant of time depend on the present inputs as well as on the past outputs are called sequential circuits. In sequential circuits, the output signals are fed back to the input side. A block diagram of a sequential circuit is shown in Figure 7.1


Figure 7.1
Block diagram of a sequential circuit.

From Figure 7.1, we find that it consists of combinational...


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Digital Multimeters
Digital multimeters (or multi-meters) are used to measure electrical quantities such as voltage, current, resistance, frequency, temperature, capacitance, and time period measurements.
Microcontrollers (MCU)
Microcontrollers (MCU) are complete computer systems on a chip. They combine an arithmetic logic unit (ALU), memory, timer/counters, serial port, input/output (I/O) ports and a clock oscillator.
Programmable Logic Devices (PLD)
Programmable logic devices (PLD) are designed with configurable logic and flip-flops linked together with programmable interconnect. PLDs provide specific functions, including device-to-device interfacing, data communication, signal processing, data display, timing and control operations, and almost every other function a system must perform.
Simple Programmable Logic Devices (SPLD)
Programmable logic devices (PLD) are digital devices with configurable logic and flip-flops linked together with programmable interconnect.
Field-Programmable Gate Arrays (FPGA)
Field-programmable gate arrays (FPGAs) have a different architecture than SPLDs and CPLDs, and typically offer higher capacities. FPGAs are also known as logic cell arrays (LCA) and programmable ASIC (pASIC).

Topics of Interest

A register is a group of binary storage cells capable of holding binary information. A group of flip-flops constitutes a register, since each flip-flop can work as a binary cell. An n-bit register,...

7.1 INTRODUCTION So far, all of the logic circuits we have studied were basically based on the analysis and design of combinational digital circuits. Though these type of circuits are very important,...

5.1 INTRODUCTION The digital system consists of two types of circuits, namely Combinational circuits and Sequential circuits A combinational circuit consists of logic gates, where outputs are at any...

The digital system consists of two types of circuits, namely (i) Combinational circuits and (ii) Sequential circuits A combinational circuit consists of logic gates, where outputs are at any instant...

5.5 Sequential Logic Design 5.5.1 Introduction Sequential logic circuits are based on combinational logic circuit elements (AND, OR, etc.) working alongside sequential circuit elements (latches and...

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