This document discusses multiplexers, which take multiple input signals and steer one of the inputs to the output based on control signals. It provides examples of 4-to-1, 16-to-1, and 8-to-1 multiplexers and describes how their outputs are determined by the states of the control signals. It also describes the IC 74150 16-to-1 multiplexer chip and the nibble multiplexer, which selects between two 4-bit nibbles as its output.
2. MULTIPLEXER
Multiplexer means many into one
Many inputs, only one outputs
Control signals steer any input to the output
Also called data selector
General idea & general circuit
n – input signals
m – control signals
1- output signals
m control signals select 2m input signals
= n < 2m
3. 4 - to - 1 Multiplexer
Depending on control inputs A & B = one of the four inputs D0 to D3 steered to
output Y
SOP Operation
Y = A B D0 + ABD1 + ABD2 + ABD3
If A = 0, B = 0
Y = 0 0 D0 + 0 0 D1 + 0 0 D2 + 0 0 D3
Y = 1 1 D0 + 1 0 D1 + 0 1 D2 + 0 0 D3
Y = D0
A = 0, B = 0 == upper AND gate is active, others inactive
Y = D0
A = 0, B = 1 == Second AND gate is active, others inactive
Y = D1
A = 1, B = 0 == Third AND gate is active, others inactive
Y = D2
A = 1, B = 1 == Fourth AND gate is active, others inactive ====== Y = D3
4.
5. 16 - to - 1 Multiplexer
Inputs = D0 to D15
When ABCD = 0000, Upper AND = active, other gates = disabled, D0 transmitted
to output
Y = D0
If D0 = 0, Y = 0, If D0 = 1, Y = 1
The value Y depends on D0
When ABCD = 1111, Lower AND gate is active, others inactive
Y = D15
Output Y =
8 - to - 1 Multiplexer
Inputs = D0 to D7, Three control inputs
When ABC = 000, Y = D0
ABC = 001, Y = D1
ABC = 010, Y = D2 ……………………….. ABC = 111, Y = D7
6.
7. IC 74150
16 - to - 1 TTL multiplexer, 24 pin IC
Pin 1 to 8 & 16 to 23 ===== D0 to D15
Pin 11, 13, 14, 15 ======= A, B, C, D
Pin 10 = output = complement of the selected data bit
Pin 9 = Strobe = enables or disables the input
Low strobe = enable the multiplexer ====== Y = Dn
High strobe = disable the multiplexer ====== Output = high === value of
ABCD doesn’t matter
Two standard methods for implementing truth table
1. Sum of products
2. Product of sum
3. Third method is multiplexer solution
i.e., complementing each Y output = data input
8.
9. Multiplexer Logic
Complementing each Y output = data input
1. D0 = î = 0
2. D1 = ô = 1 ……………. D15 = î = 0
Bubbles on Signal lines
Bubble on the line = complement
Bubbles = indicate active low signal
Nibble Multiplexer
Input = 4 bits = nibble = A3A2A1A0 = B3B2B1B0
SELECT = determine which nibble is transmitted to output
SELECT = Low = Four NAND gates on left activated
Y3Y2Y1Y0 = A3A2A1A0
SELECT = High = Four NAND gates on right activated
Y3Y2Y1Y0 = B3B2B1B0
10. Nibble Multiplexer – IC 74157
Has Strobe input
Strobe is active low input
Strobe = low ==== multiplexer is active
Strobe = high ==== multiplexer is inactive