7. Sequential circuits, 2nd part

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7. Sequential circuits, 2nd part

• Objectives To recognize and know to use the
  principal types of sequential circuits
• Registers
• Counters
• Generators of imposed sequences

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Registers

• Are sequential circuit capable of storing
  information of several bits (word).
• Made of a set of flip-flops of the same type,
  driven by the same clock pulse.
• There can be external gates to control the inputs
  of the flip-flops.

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4 bits Register with D flip-flops
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Registers (II)

• Contents series of bits
• Length a number of flip-flops
• The flip-flops used usually transition on the
  clock pulse (ascending or descending).
• Any sequential circuit can be made up of
  registers!

5
Registers (III)

• A register preserves the state!

Value of the next state
Combinational Circuit
Register (state)
C
Inputs
Outputs
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Realization with register ROM

• Design the following sequential circuit using a
  ROM and of a register
• A1(t1)(A1,A2,x) A1x
• A2(t1)(A1,A2,x) A2 Å x
• y(A1,A2,x) A2 x
• Let us find the canonical SOP form

Sm(4, 6) Sm(1, 2, 5, 6) Sm(3, 7)
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Realization with register ROM

• 8x3 ROM and 2 bits registers (D flip-flops )

ROM8x3
D1 A1 Q1 D2 A2 Q2
0
22
1
21
x
y
2
20
C
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Calculation of the following state and y
Transition Table
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Calculation of next state and y
Transition Table
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Programming of the ROM
Programming Table
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Programming of the ROM
Count of transition just as it is!!!(with D
flip-flops only)
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Several types of registers

• Shift registers
• one-way (left or right-hand side)
• bidirectional
• Shift registers with loading
• series or parallel
• Built with RS, D, T, JK flip-flops
• From 1, 2, 3, 4, 8, 16 N bits

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Counters

• Goes through a predetermined sequence of states.
• Made up of flip-flops .
• Useful in counting, the division of frequency of
  clock, and in the generation of unspecified
  sequences.

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Counters (II)

• They have various characteristics
• Coding
• binary, decimal, modulo M
• Mode
• Asynchronous (ripple counter)
• synchronous (all on the same clock signal)
• With loading (or not)
• Self-correcting (or not)

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Additional readings

• In Mano and Kime
• Sections 5.1 to 5.3 registers
• Sections 5.4 to 5.6 counters
• Sections 7.1 to 7.5 transfer between registers