Transcript Digital Logic

TDC 311
Digital Logic
Truth Tables
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AND
OR
NOT
NAND
NOR
XOR
XNOR
Going from a truth table to a circuit
A
0
0
0
0
1
1
1
1
B
0
0
1
1
0
0
1
1
C
0
1
0
1
0
1
0
1
M
0
0
0
1
0
1
1
1
Is this circuit reduced?
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Can apply Boolean algebra
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Or use a Karnaugh Map
Common IC chips
Common chip terminology
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SSI: 1-10 gates
MSI: 10-100 gates
LSI: 100-100K gates
VLSI: >100K
DIP
TTL
MOS
CMOS
Two Types of Digital Circuits
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Combinational circuits – a series of
logic gates
Sequential circuits – a set of logic
gates with feedback
Let’s look at some common
combinational circuits
Multiplexor
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Control lines A,B,C control which
input goes to output
Decoder
Comparator
One-bit Half Adder
One-bit Full Adder
One-bit ALU
Sequential Circuits
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Used in computer memories
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Basic unit called a latch
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Circuits with feedback
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Circuits move thru states
SR Latch
S
Q
S R Q ~Q
0 0 don’t
0 1 1
0
1 0 0
1
1 1 stable
~Q
R
NAND gates can also be NOR gates
(or no change
or quiescent)
Clocked D Latch
Q
D
Clock
~Q
Section of Computer Memory
Memory Chip
512K by
8
4096K
by 1
Memory
chip
Memory
chip