数电课件第6次课

The most simple AND OR expression
A
&
&
&
Y
4
&
B
Logical conversion Realizes with
the Exclusive
5
gate A
Logical map
Y AB
=1
Y
B
Figure 4–51 Karnaugh map minimization of the segment-a logic expression.
Y AB BC CA
3
3
ABC
Y
Truth
000
0
table
001
0
010
0
4
011
1
The logic 1 0 0
0
function
101
1
of circuit 1 1 0
1
111
1
When the input variables have two or three 1 in A, B, C, the outputs Y is 1,otherwise Y is 0, therefore this electric circuit is 4 one kind combination circuit for 3 people voting use:as long as 2 or 3 tickets agreed, the vote passes.
&
Y &
simpli fied
Logical expression
2
The most simple AND OR expression
C
&
Y1 AB Y2 BC Y3 CA
1
Y Y1Y2Y3 AB BC AC
2
Y B BC CA
The most simple AND OR expression
I0
In- I1
put …
… …
In-1
Combination circuit
Y0
… …
Y1 Out
… -put
Ym-1
The analysis method of combination circuit
Logical map
A
&
Write out it from
level
1 input to output by B
Review
• Karnaugh Map • Basic Combinational Logic Circuits • Implementing Combinational Logic • Logic Circuit Operation with Pulse Waveform Inputs
Combination circuit:
Exhaustion method
The design method of combination circuit
The circuit Example：Design a logic circuit which has switchings at function upstairs and downstairs to control the stair light， turns on expression the electric lamp with the downstairs switching before going upstairs, turns off the electric lamp after going upstairs；or turns on the electric lamp with the upstairs switching before going downstairs, turns off the electric lamp after going downstairs. 1 Suppose the upstairs switch is A, the downstairs switch is B the light is Y. And suppose when A or B is closed,Y is 1, otherwise is 0; when it bright, Y is 1, otherwise Y is 0. Lists the truth table according to the logical request.
The basic multiplexer has several data-input lines and a single output line.
Figure 4–52 The minimum logic implementation for segment a of the 7-segment display.
The widely used chips are listed in 74LS Series.
Chapter 6 Functions of Combinational Logic
The output is only decided by the input, and has no relation with the circuit current condition, and has no feedback loop in the electric circuit structure (no memory).
Truth table
A
B
Y
0
0
0
0
1
1
1
0
1
1
1
0
2
2
The most
Logical expression
Y AB AB
simple AND
or karnaugh map
OR
Realizes with
expression
3
the NAND gate Y AB AB already
Simplify
Main Contents
• Adders • Comparators • Decoders • Encoders • Multiplexer / Demultiplexers
Sec.6.8 Multiplexers (Data Selectors)
A multiplexer is a device that allows digital information from several sources to be routed onto a single line for transmission over that line to a common destination.