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Digital Electronics
Principles & Applications
Seventh Edition
Roger L. Tokheim
Chapter 9
Shift Registers
©2008 The McGraw-Hill Companies, Inc. All rights reserved.
INTRODUCTION
• Overview of Shift Registers
• Characteristics of Shift Registers
• Serial/Parallel Data Conversion
• Serial Load Shift Register
• Parallel Load Shift Register
• Recirculating Shift Register
• Using the 74194 Shift Register IC
• Digital Roulette Game
• Troubleshooting Hints
©2008 The McGraw-Hill Companies, Inc. All rights reserved.
Overview of Shift Registers
• A shift register is a sequential logic device
made up of flip-flops that allows parallel or
serial loading and serial or parallel outputs
as well as shifting bit by bit.
•
Common tasks of shift registers:
– Serial/parallel data conversion
– UART (an example)
– Time delay
– Ring counter
– Twisted-ring counter or Johnson counter
– Memory device
©2008 The McGraw-Hill Companies, Inc. All rights reserved.
Characteristics of Shift Registers
• Number of bits (4-bit, 8-bit, etc.)
• Loading
– Serial
– Parallel (asynchronous or synchronous)
• Common modes of operation.
– Parallel load
– Shift right-serial load
– Shift left-serial load
– Hold
– Clear
• Recirculating or non-recirculating
©2008 The McGraw-Hill Companies, Inc. All rights reserved.
Serial/Parallel Data Conversion
Shift registers can be used to convert from serialto-parallel or the reverse from parallel-to-serial.
Parallel out
Parallel out
Serial in
0 11 00 11 11 11 11
11
0
1 0 1 0 1 1 1 1
Serial out
Serial out
Parallel in
©2008 The McGraw-Hill Companies, Inc. All rights reserved.
QUIZ
Q#1This
represents
aa___
register.
Q#2This
represents
___
register.
Q#3This
represents
a
___
register.
Q#4- This
represents
a
___
register.
a.a. Parallel-in,
parallel-out
Parallel-in,
parallel-out
a.a. Parallel-in,
serial
Parallel-in,
serialout
out
b.
Serial-in,
parallel-out
b.
Serial-in,
serial-out
b.
parallel-out
b. Serial-in,
Parallel-in,
parallel-out
ANS:
serial-in
parallel-out
ANS:
serial-in
serial-out
ANS:
parallel-in
serial-out
ANS: parallel-in parallel-out
©2008 The McGraw-Hill Companies, Inc. All rights reserved.
Serial Load Shift Register
Parallel outputs here.
Order= A B C D
1 1
0
0 0
1 0
1
Data =
=0
1
Data
4-bit
serial-in
parallel out
shift right
shift register
Inputs here:
Clock input:
(1) Data Clock Pulse 2
3
4
6
7
Positive-edge
Clock Pulse 1
5
8
(2) Clock
Clear
input:
triggering
(3) Clear
Active =
0 =1
0
Clear
Deactivated = 1
Note the use of D FFs.
Clock (CLK) inputs wired in parallel.
Clear (CLR) inputs can be activated with LOW
or disabled with HIGH.
Preset (PS) inputs deactivated.
©2008 The McGraw-Hill Companies, Inc. All rights reserved.
QUIZ
QUESTION #7
#2
#3
#4
#6
#5
QUESTION #1
What is the 4-bit output (bit A on left, D on right) after pulse 6?
1?
2?
3?
5?
4?
This is a ___ type shift register.
A. Serial-in, parallel out
A: Serial-in,A:
A:parallel-out
0100
1000
1100
0000
0010
1001
B. Parallel-in, serial-out
Data
Data =
=1
1
00
Data
Data
=
1
Clock
ClockPulse
Pulse
Pulse26
4
Clock
Clock
Pulse
5
13
Clear
Clear
Clear =
=
=1
1
1
Clear
01
©2008 The McGraw-Hill Companies, Inc. All rights reserved.
Parallel Load Shift Register
Outputs here.
Order= A B C D
Parallel data
inputs
(Active LOW)
Recirculating
lines:
Pass
data
Note
thefrom
FFD to FFA
recirculating
on
each
lines.
clock pulse.
Clock input- H-to-L
Clear input- Active LOW
Note the use of J-K FFs.
Clock (CLK) inputs wired in parallel.
Clear (CLR) input activated with LOW.
Parallel load inputs (A,B,C,D) are active LOW.
©2008 The McGraw-Hill Companies, Inc. All rights reserved.
Recirculating Shift Register
11
0
00
10
1
Parallel
Paralleldata
datainputs=
inputs=
only
C&
allD
D
Binactive
activated
activated
active
Clock
pulse8 7
1
2
3
5
6
Clockpulse
4
Clear
input=1 0
1
Clearinput=
©2008 The McGraw-Hill Companies, Inc. All rights reserved.
QUIZ
Q#1After
clock
pulse
1,2,the
output
from
the
shift
register
Q#2After
clock
pulse
the
output
from
the
shift
register
Q#3After
clock
pulse
3,
the
output
from
the
shift
register
Q#4After
clock
pulse
4,
the
output
from
the
shift
register
will
Q#5be
___.
After
clock
pulse
5,
the
output
from
the
shift
register
will
Q#6be
___.
After
clock
pulse
6,
the
output
from
the
shift
register
will
be
___.
will
be
___.
will
willbe
be___.
___.
0011001100
1
1
000010011001
Parallel data inputs=
Bnone
and Cactive
active
Clock pulse 6
1
2
3
4
5
Clear input= 1
0
©2008 The McGraw-Hill Companies, Inc. All rights reserved.
Universal Shift Register IC
Outputs here
Clear input
Serial data Rightactive
input LOW
used during
Serial Load Right
mode ofdata
operation
Parallel
inputs
Order: A, B, C, D
Serial
Leftloading
input
during data
Parallel
used during
Serial Load Left
mode of operation
Clock input
Mode
Controls:
L-to-H
triggering
Hold
Parallel load
Shift right
Shift left
74194 Universal 4-bit Shift Register IC.
Modes of operation: Hold, Parallel load, Shift right & Shift left.
An active LOW Clear (CLR) input overrides all others.
©2008 The McGraw-Hill Companies, Inc. All rights reserved.
Using the 74194 Shift Register IC
1 0
0
1 1
0 0
1
CLR = 1
0
Serial R = X
0
Parallel Load=
010
10
Serial L = 0
X
1
Clock pulse 8
1
2
3
4
5
6
7
(L-to-H)
S0= 0
1
S1= 1
0
X = Irrelevant
©2008 The McGraw-Hill Companies, Inc. All rights reserved.
QUIZ
QUESTION
QUESTION#3
#1
#2
#5
#6
#7
QUESTION #4- What is the mode of operation during and the output of the
The
What
What
74194
isisthe
the
IC
mode
mode
could
of
of
be
operation
operation
described
during
during
as a 4-bit
and
andthe
the
(shift
output
output
right,
of
of
universal)
the
the
shift register after pulse 3?
shift
shiftregister
register.
registerafter
afterpulse
pulse2?
1?
4?
5?
6?
A:right,
Universal
A:A:A:
Parallel
A:
A:
Shift
Shift
Clear,
Hold,
left,
load,
0000
1
0
001
0
010
1
101
00
? ? ? ?
0
CLR = 1
X
Serial R = 0
Parallel Load=
0100
Serial L = X
1
1
2
4
Clock pulse 6
3
5
(L-to-H)
1
S0= 0
0
S1= 1
©2008 The McGraw-Hill Companies, Inc. All rights reserved.
Digital Roulette Game
Audio
Amplifier
0
1
0
Power-up
Initializing
Circuit
Spin
Wheel
+5V input
Voltage
Controlled
Oscillator
(VCO)
1
0
1
0
0
1
1
0
1
0
8-bit
Ring Counter
(shift register)
1
0
1
0
Simulated
Roulette
Display
©2008 The McGraw-Hill Companies, Inc. All rights reserved.
QUIZ
Q#1The block
at ABininthe
digital roulette
game
Q#2Q#3- The
Theblock
blockat
at C inthe
thedigital
digitalroulette
roulettegame
game
contains
a(n)
___
circuit.
contains
containsa(n)
a(n)___
___circuit.
circuit which is a type of 8-bit shift register.
ANS: voltage-controlled
oscillator (VCO)
ANS:
ANS:audio
ringamplifier
counter
B
A
C
©2008 The McGraw-Hill Companies, Inc. All rights reserved.
Simple Troubleshooting Hints
• Feel top of IC to determine if it is hot
• Look for broken connections, signs of
excessive heat
• Smell for overheating
• Check power source
• Trace path of logic through circuit
• Know the normal operation of the circuit
©2008 The McGraw-Hill Companies, Inc. All rights reserved.
QUIZ
1. The most important factor in successful
troubleshooting is a good knowledge of the
circuit’s normal operation. (True or False)
2. The first three steps in troubleshooting are to
use your senses to (1) __________ the top of the
ICs for overheating, (2) look for broken
connections, and (3) smell for signs of
overheating.
3. The fourth step in troubleshooting is to use
a(n) __________ (logic probe, tachometer) to
check the power sources to the IC.
4. The fifth step in troubleshooting is to trace
the path of logic through the circuit. (True
or False)
True
feel
logic probe
True
©2008 The McGraw-Hill Companies, Inc. All rights reserved.
REVIEW
• Overview of Shift Registers
• Characteristics of Shift Registers
• Serial/Parallel Data Conversion
• Serial Load Shift Register
• Parallel Load Shift Register
• Recirculating Shift Register
• Using the 74194 Shift Register IC
• Digital Roulette Game
• Troubleshooting Hints
©2008 The McGraw-Hill Companies, Inc. All rights reserved.