MSI Components

Integrated Circuit

Also known as IC, chip, or microchip

Set of electronic circuits on one small flat piece of semiconductor material

Scale of integration

Number of components fitted into standard size IC.

Decoder

Decoder

Input: a code (from input lines) Output: output lines.

n-to-m, n:m, n x m

n-bit codedecoderup to output lines

Each output of a decoder is a minterm of a variable function.

Implementing functions

A Boolean function in sum-of-minterms form can utilise a decoder to generate the minterms, and an OR gate to form the sum.

Any combinational circuit with inputs and outputs can be implemented with an decoder with OR gates.

Good when circuit has many outputs, and each function is expressed with a few minterms.

Enable

Decoders often come with an enable control signal so that device is only activated when .

Constructing Larger Decoders

Larger decoders can be constructed from smaller ones.

2x4DECwxy2x4DEC

MSI Decoder



Encoding

Encoder

Input: input lines Output: bits of code

XYF0F1F2F30010000101001000101100014x2 encoder(the rest are don't cares)With this, we can obtain:F0F1F2F3YX

At any one time, only one input line of an encoder has a value of 1 (high), the rest are 0 (low).

Priority Encoders

A priority encoder is one with priority

• if two or more inputs, inputs with highest priority takes precedence:

Multiplexers

Helps share a single communication line among a number of devices. Only one source and one destination can use the communication line.

Demultiplexer

Demultiplexer

Directs data from input to one selected output line.

Input: Input line, set of selection lines Output: Data from input to one selected output line

demuxselection linesdataoutputs

Demultiplexer circuit is identical to a decoder with enable.

Multiplexer

Multiplexer

(Data selector)

Input: A number of input lines, a number of selection lines Output: Data to one output line - sum of (product of data lines and selection lines)

A -to--line multiplexer - MUX is made from an decoder by adding to it input lines, one to each AND gate:

2-to-4Decoder0123Y

Larger Multiplexers

Larger multiplexers can be constructed from smaller ones.

4:1MUX4:1MUX2:1MUX

Implementing Functions

A -to-1 multiplexer can implement a Boolean function of input variables,

1. Express function in sum-of-minterms form
2. Connect variables to the selection lines
3. Put a 1 on a dataline if it is a minterm of the function, and 0 otherwise.

Using Smaller Multiplexers

1. Express Boolean function in sum-of-minterms-form
2. Reserve one variable for input lines of MUX, and use the rest for selection lines
3. Draw truth table for function, by grouping inputs by selection line values, then determine multiplexer inputs by comparing input line and function for corresponding selection line values.

if C is the chosen line, note the F output for C = 0,1 for each input line.