Decoder, Encoder, Multiplexer, Demultiplexer, ROM, PLA

1. Logic Devices

2. Decoder
• A decoder is a combinational circuit that
converts binary information from n inputs to
2 𝑛
unique output lines.
If input=2, output=4
If input=3, output=8

3. 2-to-4 Decoder

4. 3-to-8 Decoder

5. Implementation of a full adder with a
decoder

7. Encoder
• An encoder has 2 𝑛
input lines and n output
lines.

8. 4-to-2 Encoder

9. 8-to-3 Encoder

10. Multiplexers
• A multiplexer is a combinational circuit that
selects binary information from one of many
input lines and directs it to a single output
line.
• The selection of a particular input line is
controlled by a set of selection lines. Normally.
there are 2 𝑛
input lines and II selection lines

11. Multiplexers
2 to 1 line multiplexer 4 to 1 line multiplexer

12. Demultiplexers
• It has one input line, n selection lines and 2 𝑛
output lines.

13. ROM
• ROM= Read Only Memory
• It is a device that includes both decoder and
OR gates.
• It consists of n input lines and m output lines.

14. Types of ROMs
1. PROM= Programmable read only memory
when ordered, PROM units contain all 0’s or
all 1’s.
2. EPROM= Erasable PROM
when an EPROM is placed under a special uv
light for a given period of time, the short-
wave radiation discharges the internal gates
that serve as contacts. After erase, the ROM
returned to its initial state.

15. 3. EAROM= Electrically alterable ROM
This ROM can be erased with electrical signals
instead of uv light.

16. Programmable Logic Array(PLA)
• A programmable logic array (PLA) is a kind of
programmable logic device used to implement
combinational logic circuits.
• The PLA has a set of programmable AND gate
planes, which link to a set of programmable
OR gate planes, which can then be
conditionally complemented to produce an
output.

17. Block diagram of PLA

18. Thank you