Notes 5

Question 1

decoders

Answer 1

converts binary to one hot

the binary number of the input makes the Yi output hot (1)

Question 2

2 to 4 decoder truth table

Answer 2

A1 A0 | Y3 Y2 Y1 Y0
0 0 0 0 0 1
0 1 0 0 1 0
1 0 0 1 0 0
1 1 1 0 0 0

Y0 = A1’A2’
Y1 = A1’A0
Y2 = A1A0’
Y3 = A1A0

Question 3

primary encoders

Answer 3

gives a signal for which button was pressed

signals the highest number

deals with the question of what happens of two buttons are pressed

converts one hot to a binary number

Question 4

priority encoders truth table 4 to 2

Answer 4

Y3 Y2 Y1 Y0 | V A1 A0
0 0 0 0 0 X X
0 0 0 1 1 0 0
0 0 1 X 1 0 1
0 1 X X 1 1 0
1 X X X 1 1 1

first line is not valid because no buttons were pushed

V stands for valid

Question 5

enable can be thought as an

Answer 5

on off switch

Question 6

enable 4to2 decoder truth table

Answer 6

if enable if 0 then everything if off

if enable is 1 then proceed like a regular 4 to 2 decoder

E A1 A0 | Y3 Y2 Y1 Y0
0 0 0 0 0 0 0
0 0 1 0 0 0 0
0 1 0 0 0 0 0
0 1 1 0 0 0 0
1 0 0 0 0 0 1
1 0 1 0 0 1 0
1 1 0 0 1 0 0
1 1 1 1 0 0 0

Question 7

make block diagram for 4 to 2 decoder

Question 8

draw how encoders and decoders work together using a block diagram

Question 9

multiplexers

Answer 9

MUXs

used to select one of multiple possibilities

a hardware “if” statement

Question 10

2 to 1 MUX

Answer 10

if S0 is off Z = A
if S0 is on Z = B

Question 11

truth table for 2 to 1 mux

Answer 11

S0 A B | Z
0 0 0 0
0 0 1 0
0 1 0 1
0 1 1 1
1 0 0 0
1 0 1 1
1 1 0 0
1 1 1 1

use k map to make circuit

Question 12

4 to 1 mux

Answer 12

S1 S0 | Z
0 0 A
0 1 B
1 0 C
1 1 D

can make truth table and kmap for this as well to create the circut

Question 13

Build a 4-1 mux using three 2-1 muxes

Answer 13

draw it

Question 13

block diagram for Muxs

Answer 13

draw it

Question 14

how are muxes helpful

Answer 14

you can make any circuit using muxes, can divide and conquer

split table into half, quarters, eighths, ect
find selector bits