So far we have defined basic building blocks as - PowerPoint PPT Presentation

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So far we have defined basic building blocks as

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Using building blocks to make bigger circuits. 2. Flip-flops can be connected to act as a register ... get different input, each storing one-bit information ... – PowerPoint PPT presentation

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Title: So far we have defined basic building blocks as


1
Using building blocks to make bigger circuits
  • So far we have defined basic building blocks as
  • Inverter, AND, and OR gates
  • storage elements (D-Flip-flop)
  • These building blocks can be used to bigger
    circuits
  • We may give them additional functionality
  • We can either add more inputs or wider inputs,
    and outputs
  • Or we may perform a more complex operation
  • Or both, like multiplexers, decoders, .
  • Examples
  • 3, 4, 5 . n bit input gates
  • Or you may have multiple bit data inputs
  • AND, OR, XOR, STORE, READ n-bit data

2
Making a register
  • Flip-flops can be connected to act as a register
  • All clock signals are connected together to one
    clock
  • All flip-flops get different input, each storing
    one-bit information
  • A 4-bit register is shown -- It uses 4 D-FFs
  • Has a 4 bit inputs and 1 clock and produces 4 bit
    output

3
Making a shift-register
  • Flip-flops can also be connected to act as a
    shift register
  • All clock signals are connected together to one
    clock
  • First flip flop gets a new input
  • Others get input from previous flip-flop
  • A 4-bit shift register is shown
  • It has one bit and one clock input and produces 1
    bit output

4
Using 1-bit building blocks to make n-bit circuit
  • Design a 1 bit circuit with proper glue logic
    to use it for n-bits
  • It is called a bit slice
  • The basic idea of bit slice is to design a 1-bit
    circuit and then piece together n of these to get
    an n-bit component
  • Previous two examples showed how to use 1-bit
    components
  • However, there was no other glue signal or logic
  • Next, we consider other kind of examples
  • A half-adder adds two 1-bit inputs
  • Two half adders can be used to add 3 bits
  • A 3-bit adder is a full adder

5
Full adder and multi-bit adder
  • Two half adders can be used to add 3 bits
  • n-bit adder can use full adders
  • n can be arbitrary large

6
Glue Logic
  • Normally the glue logic is part of 1-bit adder
  • A basic building block has
  • Primary inputs
  • Primary outputs
  • Cascading inputs
  • Cascading outputs
  • The cascading signals interact directly with the
    glue logic
  • Carry in 1-bit adder is a primary as well as a
    cascading output
  • A and B are primary inputs
  • C is a cascading input
  • Cout is cascading output
  • S is primary output
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