Registers and Counters

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Registers and Counters PHE-10
Prabhakar Singh School of Sciences Indira
Gandhi National Open Unievsrity Maidan Garhi, New
Delhi-110068
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Basic Definitions
Registers
It is a sequential logic
circuit containing filp-flops arranged in a
certain predetermined faishon in order to store
and transfer data in digital systems.
Counters
A counter is a sequential
logic circuit consisting of a set of flip-flops
which can go through a sequence of states.
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Digital Logic Circuits
Combinational Logic Circuit
Sequential Logic Circuits
Memory element
Yn f(Xn)
(one bit memory element)
Yn f(Xn, Yn-1)
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Flip-Flop
A one bit storage cell
Truth Table Of NAND gate
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S-R Flip-Flop
Truth-table of S-R flip-flop
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Clocked S-R Flip-Flop
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How to remove the ambiguous (?) state in S-R
flip-flop
Solution
J-K Flip-flop
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Preset and Clear
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Edge triggered flip-flops
Positive edge triggered
Negative edge triggered
Level triggered
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D-type Flip-flop
T-type Flip-flop
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Registers
Shift Registers
BufferRegisters
Store digital data
Store digital data
Allow shifting (operation)of the data
No operation on data
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Controlled Buffer Register
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Shift Registers

• Serial in ParalleI out

• Serial in Serial out

• Parallel in Serial out

• Parallel in Parallel out

Universal Shift Register
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U N I V E R S A L S H I F T R E G.
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Counters
Synchronous counters
Clock pulse is applied to each FF simultaneously
The output of one FF drives the input of the
next one
High Speed
Slow speed
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Modulus (mod) of the counters
Mod 16 counter
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Output of a FF will changes if the clock goes
from high (1) to low (0) state
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Decade Counter (Mod 10)
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For Mod-9 counter?
91001
For Mod-13 counter?
131101
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Synchronous Counter

• Clock pulse is applied to all the FFs
• simultaneously

• The inputs of the FFs depends on the present
• state as well as the next state of the output

• Knowledge of Karnaugh (K) map may be
• required to determine the values of inputs

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Summary

• Registers and counters are the sequential logic
  circuits.

• Flip-flops are the basic building block of these
  circuits.

• Buffer registers are used to store the digital
  data,
• no shifting of data is allowed.

• Shifting of data can be achieved using shift
  registers.

• Ripple counters are easy to construct but are
  slow
• in speed.

• Synchronous counters are fast as the clock is
  applied
• simultaneously on each FFs