EGR 277

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Lecture 17 EGR 277 Digital Logic
Reading Assignment Chapter 6 in Digital Design,
3rd Edition by Mano

• Timing Sequences
• So far we have designed circuits to
• produce desired outputs for certain input
  combinations (combinational circuits)
• produce a desired sequence of states or input
  output sequence (sequential circuits)
•  
• One type of circuit that we have not directly
  dealt with is a circuit that will produce a
  series of control signals (or timing sequences)
  where each signal is HIGH or LOW for a specified
  length of time.
• Such timing sequences are often needed. Examples
  might include
• signals to stop, start, and control the length
  of time for each cycle in a washing
• machine
• signals to control the RED, YELLOW, and GREEN
  signals for a stop light
• signals to control the opening and closing of
  valves

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Lecture 17 EGR 277 Digital Logic
Decoders Can be used to indicate when certain
counts occur. Similarly, they can be used to
start or stop events at certain times.
Example Design a decoder to detect when count 4
occurs.
Example Design a decoder to detect when counts
5, 7, or 15 occur. Also show how a 4x16 decoder
could be used.
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Lecture 17 EGR 277 Digital Logic
Example Design a circuit that will output a
signal that is HIGH for 3 seconds and LOW for 5
seconds.
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Lecture 17 EGR 277 Digital Logic
Example Design a circuit that will produce the
following control signals.
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Lecture 17 EGR 277 Digital Logic
Example Design a traffic light controller with
the following control signals.
Notes Whenever N/S Green or N/S Yellow are HIGH,
E/W Red must also be HIGH. Whenever E/W Green or
E/W Yellow are HIGH, N/S Red must also be
HIGH. Handout Traffic Light Controller
schematic and PSPICE implementation Demo
Traffic Light Controller Circuit
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Lecture 17 EGR 277 Digital Logic

• Shift Registers
•  
• Register - a group of binary storage cells
  (flip-flops)
•  
• Common Register Uses
• Temporary data storage and transfer
• Parallel-to-serial and serial-to-parallel
  conversion
• Data manipulation (complementation, rotation,
  etc)
•  
• Shift register - A register is often also
  referred to as a "shift register" since one of
  its
• key functions involves the shifting of data
  through the register.

Example A register might be a group of 8
flip-flops used to store some binary data (byte
or word). Sketch the circuit.
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Lecture 17 EGR 277 Digital Logic
Example A computer or microprocessor uses many
types of registers, includingCPU, PC, SP, ALU
(with registers A and B), C, D, E, F (general
purpose), I/O registers at ports, etc. Sketch.
Also show some common assembly language
instructions involving registers.
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Lecture 17 EGR 277 Digital Logic
Common register functions (briefly illustrate
each) 1) Serial shifting of data (SISO - right or
SISO - left) (SISO Serial-input,
Serial-output) 2) Parallel input of data
(PI) 3) Parallel output of data
(PO) 4) Rotation of data (left or right)
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Lecture 17 EGR 277 Digital Logic
Parallel load shift register using D flip-flops -
illustrate
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Lecture 17 EGR 277 Digital Logic
Parallel load shift register with an enable
Discuss the limitations of the prior shift
register. Show how to implement the register
above using SR or JK flip-flops and then add an
enable (ANDed with each input).
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Lecture 17 EGR 277 Digital Logic
Serial-In Serial-Out (SISO) register Illustrate
using D flip-flops and JK flip-flops.
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Lecture 17 EGR 277 Digital Logic
Rotation of data Illustrate rotate-right and
rotate-left registers using D flip-flops and JK
flip-flops.
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Lecture 17 EGR 277 Digital Logic
Multi-function shift register Design a shift
register with two mode controls, x and y, that
will function as follows
Show how to provide the input connections using
logic gates or multiplexers
Handout 7495 Data Sheet. Discuss the features
available on this 4-bit shift register.