MSI Components

Introduction

Integrated Circuit

• set of electronic circuits on one small flat piece of semiconductor material

Scale of integration

• the number of components fitted into a standard size IC

#ssi msi lsi vlsi ulsi

Decoders

Convert binary information from n input lines to a maximum of $2^n$ output lines

2x4 Decoder

• selects an output line based on the 2-bit code supplied.
• 

3x8 Decoder

• outputs represent the minterms

Implementing Functions

• A boolean function, in sum-of-minterms form →
  • decoder to generate the minterms, and
  • an OR gate to form the sum
• Any combinational circuit with n inputs and m outputs can be implemented with an $n:2^n$ decoder with m OR gates
• Good when circuit has many outputs, and each function is expressed with a few minterms
• Example of using a decoder to implement functions
• 

Decoders with Enable

• Decoders often come with an enable control signal, so that the device is only activated when the enable, E = 1
• 
• However, in most MSI decoders, the enable signal is a zero-enable.
  • If you want to use the decoder, you put a 0 instead of a 1

Constructing Larger Decoders

• you can construct larger decoders from smaller ones
• e.g. building a 3x8 decoder from two 2x4 decoder
• 

Encoders

Encoding is the converse of decoding

• takes in $2^n$ input lines and produces $n$ output.

Priority Encoders

• if two or more inputs equal to 1, the input with the highest priority takes precedence
• If all inputs are 0, this input combination is considered invalid

Demultiplexers

• given an input line and a set of selection lines, a demultiplexer directs data from the input to one selected output line.
• e.g. 1-to-4-demultiplexer
• 

Tip

Internally, a demultiplexer circuit is actually identical to a decoder with enable!

Multiplexers

• Also known as a data selector!
• A device that has:
  • a number of input lines
  • a number of selection lines
  • one output line
• It steers one of $2^n$ inputs to a single output line, using n selection lines. Also known as a data selector.
• e.g. 4-to-1-multiplexer
• 

How to implement a 4-to-1-multiplexer?

Standard MSI Multiplexer

8-to-1 multiplexer