DIGITAL COMPONENTS By Sohaib

Integrated Circuits Digital circuits are constructed with integrated circuits. An integrated circuit is a small silicon semiconductor crystal, called a chip, containing electronic components. As the technology has advanced, the number of gates that can be put into the chip has increased.

Medium Scale Integration MSI have a complexity of approximately 100 to 200 gates in a single package. They usually perform specific elementary digital functions such as decoders, adders and registers.

Large Scale Integration LSI devices contain between 200 to few thousands of gates in a single package. They include digital systems such as processors, memory chips, and programmable modules.

Very Large Scale Integration VLSI devices contains thousands of gates in a single package. Examples are large memory arrays and complex microcomputer chips. Because of their small size and low cost, VLSI devices have revolutionized the computer system design technology.

Decoders A decoder is a combinational circuit that converts binary information from n coded inputs to 2n unique outputs. A decoder has n inputs and m outputs and is also referred to as an n x m decoder. The logic diagram of 2 x 4 decoder is shown in a figure.

2 to 4 Line Decoder

Encoder An encoder is a digital circuit that performs the inverse of a decoder. The encoder can be implemented by OR gates whose inputs are determined directly from the truth table.

Encoder

Multiplexer & Demultiplexer A multiplexer is a device that receives binary information from one of 2n input data and directs it to a single output line. A demultiplexer is a combinational circuit which performs exactly the opposite operation performed by multiplexer.

Mux & Demux

Registers Registers can be used by a programmer/user to carry out calculations or other tasks performed within the CPU. All of the 8086 family of CPUs have 14, 16-bit registers that are commonly used and are at the disposal of the user. Starting with the 80386, Intel also added a new set of 32-bit registers and instructions to the CPU.

Memories (RAM) Random-access memory (usually known by RAM) is a form of computer data storage. Today, it takes the form of integrated circuits that allow stored data to be accessed in any order (i.e., at random). The word RAM is often associated with volatile types of memory (such as DRAM), where the information is lost after the power is switched off.

ROM Read-only memory (usually known by its acronym, ROM) is a class of storage media used in computers and other electronic devices. Because data stored in ROM cannot be modified (at least not very quickly or easily), it is mainly used to distribute firmware(software that is very closely tied to specific hardware, and unlikely to require frequent updates). In its strictest sense, ROM refers only to mask ROM (the oldest type of solid state ROM), which is fabricated with the desired data permanently stored in it, and thus can never be modified.