ITEC 352

Lecture 5Low level components(3)

Low level components

Review

• Multiplexers• Demultiplexer• Minterm/Maxterm• Karnaugh Map

Low level components

Outline

• Decoders • 7 Segment display

Low level components

Decoder

• Similar to a DeMultiplexer– Essential difference: the select (or control lines)

are now considered as part of input.• Used to convert logical encoding into spatial

encoding.• Decoders generate the minterms for a

function.

Low level components

A 2-4 Decoder: generates all possible minterms with 2 bits

Low level components

Majority Function

• Implement it using a decoder

Low level components

Using a Decoder to Implement the Majority Function

Low level components

Example decoder

• Example:Develop a circuit for this:

• Develop a circuit that drives one input digit for this clock radio.

Low level components

Clock radio

• Step 1: – Initial questions:• How many outputs are there for the circuit ? • How many inputs are needed to design this circuit ?

– Usually we are interested only in the minimum number of inputs.

– However, sometimes it helps us look at other inputs.» What possible other inputs can you think of ?

• Next: How are the outputs related to the inputs.

Low level components

numeric display (2)

• How are the outputs related to the inputs ?

– Capture this function using a boolean equation– How do we derive boolean equations? use truth tables.

a

b

d

ce

fg

Low level components

numeric display (3)

• Draw the truth table for matching inputs to outputs.

Low level components

numeric display (4)

• Which of the following standard circuits can you use to develop this circuit:– Decoder– Multiplexer– Demultiplexer

• Why ?

Low level components

numeric display (5)

• Decoders generate minterms.• What type of a decoder would you use:– 1 X 2– 2 X 4– 3 X 8 – Etc.. ?

Low level components

Implementation

• Logisim demonstration

Low level components

Review

• Decoders• Majority function