Transcript chapter 1

PowerPoint Overheads for
Computer Architecture
From Microprocessors To Supercomputers
Behrooz Parhami
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1.1 Signals, Logic Operator, and Gates
Figure 1.1 Some basic elements of digital logic circuits, with operator signs used in this book highlighted.
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Figure 1.2 Gates with more than two inputs and/or with inverted signals at input or output.
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Figure 1.3 An AND gate and a tristate buffer can act as controlled switches or valves. An inverting buffer is logically the same as a NOT gate.
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Figure 1.4 Wired OR allows tying together of several controlled signals.
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Figure 1.5 Arrays of logic gates represented by a single gate symbol.
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1.2 Boolean Functions and Expressions
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Truth table
– N-variable input: 2n
– x: don’t care. x in output column means no interest; x in input column means that
function does not depend on the value of the particular variable involved.
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Logic expression
– NOT takes precedence over AND
– AND takes precedence over OR/XOR
– Logic expression can be manipulated using laws of Boolean algebra in order to obtain an
equivalent logic expression for simpler or more suitable hardware realization.
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Word statement
– Natural language
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Logic diagram
– Graphical representation of a Boolean function that carries information about its
hardware realization.
– Logic circuit synthesis: derive logic diagram from truth table, logic expression, or word
statement.
– Logic circuit analysis: going backward from logic diagram to truth table, logic
expression, or word statement.
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Table 1.1 Three 7-variable Boolean functions specified in a compact truth table with don’t-care entries in both input and output columns.
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Table 1.2 Laws (basic identities) of Boolean algebra.
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1.3 Designing Gate Networks
Figure 1.6 A two-level AND-OR circuit and two equivalent circuits.
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BCD to 7-segment decoder
Figure 1.7 Seven-segment display of decimal digits. The three open segments may be optionally used. The digit 1 can be displayed in
two ways, with the more common right-side version shown.
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x3x2x1x0
e0 e1
e2
e3 e4 e5
0000
1
0001
0
0010
1
0011
1
0100
0
0101
1
0110
1
0111
0
1000
1
1001
0
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e3  x3 x2 x1 x0  x3 x2 x1 x0  x3 x2 x1 x0  x3 x2 x1 x0  x3 x2 x1 x0  x3 x2 x1 x0
 x1 x0  x2 x0  x2 x1  x2 x1 x0
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Figure 1.8 The logic circuit that generates the enable signal for the lowermost segment (number 3) in a seven-segment display unit.
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1.4 Useful Combinational Parts
• Multiplexer
– 2a input signals: x0, x0, …,xN (N=2a-1)
– Single output z
– a control signal (address signal): y0, …, ya-1
• Decoder
– a input signals
– 2a output signals
– Assert one and only one of its 2a output lines
• Encoder: opposite of a decoder.
– 2a input signals
– a output signals
– When one and only one of its 2a input lines is asserted, its
a-bit output supplies the index of the asserted input in the
form of a binary number
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Multiplexer
Y
z
0
x0
1
x1
Figure 1.9 A multiplexer (mux), or selector, allows one of several inputs to be selected and routed to output depending on the binary value of a set of
selection or address signals provided to it.
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Decoder
y1y0
X3 x2 x1 x0
00
0
0 0 1
01
0
0 1 0
10
0
1 0 0
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1
0 0 0
Figure 1.10 A decoder allows the selection of one of 2a options using an a-bit address as input. A demultiplexer (demux) is a decoder that only selects
an output if its enable signal is asserted.
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Encoder
X3 x2 x1 x0
Active
y1y0
0
0 0 1
1
00
0
0 1 0
1
01
0
1 0 0
1
10
1
0 0 0
1
11
0
xx
0 0
0 0
Figure 1.11 A 2a-to-a encoder outputs an a-bit binary number equal to the index of the single 1 among its 2a inputs.
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Programmable Combinational Parts
Figure 1.12 Programmable connections and their use in a PROM.
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Figure 1.13 Programmable combinational logic: general structure and two classes known as PAL and PLA devices. Not shown is PROM with fixed
AND array (a decoder) and programmable OR array.
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PLD: Short for programmable logic device, a generic term for
an integrated circuit that can be programmed in a laboratory to
perform complex functions.
(i) PROMs (Programmable Read Only Memory) - offer
high speed and low cost for relatively small designs
(ii) PLAs (Programmable Logic Array) - offer flexible
features for more complex designs
(iii) PAL/GALs (Programmable Array Logic/Generic
Array Logic) - offer good flexibility and are faster and less
expensive than PLAs
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Example: f = x + y + z, using circuit in Fig.13b
Figure 1.14 Timing diagram for a circuit that exhibits glitching.
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CMOS: Complementary metal–oxide–semiconductor
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The CMOS transmission gate
s
s
A (Vin )
P
N
B (Vout )
C
A (Vin )
s
MOS Circuit
The conduction path through TG is controlled by
complementary signals & s
s
In steady state
A(Vin) S
0
0
0
1
1
0
1
1
Tn
off
on
off
off
Tp
off
off
off
on
s
B (Vout )
TG Symbol
s
A
B=A
(or Z when S=0)
s
B (Vout)
Z (high impedance state (blocks logic flow))
0 (nMOS passes strong 0, pMOS off when Vout<Vthp)
Z (high impedance state (blocks logic flow))
1 (pMOS passes strong 1, nMOS off when Vout>Vdd-Vthn )
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