shift registers - ranjithchandran.com€¦ · each flip-flop in a shift register can retain one...
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Shift Registers
Registers 1.1
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Shift Register Applications
Shift Registers are an important Flip-Flop configuration with a wide range of applications, including: Computer and Data Communications Serial and Parallel Communications Multi-bit number storage Sequencing Basic arithmetic such as scaling (a serial shift to the left
or right will change the value of a binary number a power of 2)
Logical operations
Registers 1.2
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Parallel versus Serial
Serial communications: provides a binary number as a sequence of binary bits, one after another, through one data line.
Parallel communications: provides a binary number as binary bits through multiple data lines at the same time.
Registers 1.3
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Shift Registers
Shift Registers are devices that store and move data bits in serial (to the left or the right),
..or in parallel,
..or a combination of serial and parallel.
Registers 1.4
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Configuration
In Shift Registers, the binary bits transfers (shifts) from the output of one flip-flop to the input of the next individual Flip-Flop at every clock edge.
Once the binary bits are shifted in, the individual Flip-Flops will each retain a bit, and the whole configuration will retain a binary number.
Registers 1.5
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Construction
Shift registers are constructed from flip-flops due to their characteristics: Edge-triggered devices Output state retention
Each Flip-Flop in a shift register can retain one binary bit. For instance, if a 5-bit binary number needs to be stored and
shifted, 5 flip-flops are required.
Each binary bit transfer operation requires a clock edge.
Asynchronous inputs are useful in resetting the whole configuration.
Registers 1.6
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Shift Register Construction
Shift registers are comprised of D Flip-Flops that share a common clock input.
D Q
Q
D Q
Q
D Q
Q
Registers 1.7
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Combinations of Data Transfer Methods
SISO: Serial In, Serial Out
SIPO: Serial In, Parallel Out
PISO: Parallel In, Serial Out
PIPO: Parallel In, Parallel Out
How many clock edges are required for each operation?
10110 10110
10110
10110
10110
1011010110
10110
Registers 1.8
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SISO Flip-Flop Shift Register
a Serial In Serial Out shift register has a single input and a single output
D Q
Q
D Q
Q
D Q
Q
Input Output
Registers 1.9
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SIPO Flip-Flop Shift Register
a Serial In Parallel Out shift register has a single input and access to all outputs
D Q
Q
D Q
Q
D Q
Q
Input
Output Output Output
Registers 1.10
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PISO Flip-Flop Shift Register
a Parallel In Serial Out shift register requires additional gates, and the parallel input must revert to logic low.
Input
D Q
Q
InputOutput
Input
D Q
Q
D Q
Q
Registers 1.11
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PIPO Flip-Flop Shift Register
a Parallel In Parallel Out register has the simplest configuration. It represents a memory device.
D Q
Q
Input
Output
D Q
Q
Output
D Q
Q
Output
Input Input
Registers 1.12
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Universal Shift Registers
Universal Shift Registers can be configured to operate in a variety of modes. For instance, they can be configured to have either Serial or Parallel Input/Output.
Internally use steering gates to determine: Serial input/output direction Parallel input (load) Hold
Refer to the manufacturer specification sheets for more information.
Registers 1.13
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Registers 1.14
Universal Shift Registers
Look up the 74LS194 and describe its function by looking at the schematic. Fill in the table.
S0 S1 Mode0 00 11 01 1
In-class exercise14
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Application: Parallel transferring the contents of a Register to another register.
Describe where this circuit combination may be used.
Registers 1.15
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JK Shift Registers
J-K Shift registers are seldom used, as two inputs (J,K) are required to load the first flip-flop (note all others receive only set or reset inputs).
Input OutputJ Q
K Q
J Q
K Q
J Q
K QInput
Registers 1.16
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Ring Counter
A ring counter takes the serial output of the last Flip-Flop of a shift register and provides it to the serial input of the first Flip-Flop.
Ring Counters are also known as re-circulating shift registers.
The display characteristics will be familiar…
Registers 1.17
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Ring Counter
In Class: Build a ring counter using electronics simulation tools
Registers 1.18
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Self-Starting or Load on Power-up
There are several ways of loading values into a ring counter on power-up: RC circuit Logic detection (similar to truncating a counter)
Registers 1.19
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Johnson Counter
A Johnson Counter re-circulates the last flip-flop Q (inverted) output back to the input of the first Flip-Flop. It doesn’t require an initialization value, and will provide a predictable output state sequence.
Registers 1.20
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Re-Circulating Counters
Johnson Counter00001000110011101111011100110001
A 4-bit Johnson counter has a modulus of 8, meaning there are 8 unique output states.
8 unique states
Registers 1.21
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State Diagram
A State Diagram is used to describe the sequence of output states of a circuit.
The state diagram for the previous Johnson counter looks like this:
1000
1100
1110
1111
0111
0011
0001
0000
Registers 1.22
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Registers 1.23
State Recognition
One application of registers is to recognize a specific binary number. Sequences of bits are loaded in series into a register. External detection gates will identify if the value matches a predetermined value:
What value will this circuit detect?Will this work with a Johnson counter?
23
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Registers 1.24
Comparison of two values
Values stored in shift registers can be compared by using the following circuit :
What is the output be if both binary inputs are the same?24
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Assignment - 24: Q1. What is a shift register? Explain various types of shift registers.Q2. Explain Universal Register.
Registers 1.25