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Chap 8 sequencing and control l.jpg

Chap 8. Sequencing and Control

Spring 2004

Jong-Won Park

[email protected]


8 1 the control unit l.jpg

8-1 The Control Unit

  • binary information in a digital computer can be classified as either data or control information

    • data

      • manipulated in a datapath with ALUs, registers, multiplexers, and buses

    • control

      • provide signals that activate the various microoperations & determine the sequence in which the various actions are performs

  • timing of all registers in a synchronous digital system is controlled

  • by a master clock generator

    • binary variables that control the selection inputs of multiplexers, buses, ALUs, & load control inputs of registers are generated by the control unit


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8-1 The Control Unit

  • Control unit is a sequential circuit with state that dictate the control signals for the system

    • using status conditions and control inputs, the sequential control unit determines the next state, in which additional microoperations are activated

  • 2 distinct types of control units:

    programmable system & nonprogrammable system


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8-1 The Control Unit

  • programmable system

    • a portion of the input consists of a sequence of instructions

    • each instruction specifies the operation the system is to perform

    • instructions are stored in memory (RAM or ROM)

    • program counter

      • provide the address in memory of the instructions to be executed

      • address comes from a register called PC

    • executing an instruction

      • activating the necessary sequence of microoperations in the datapath that are required to perform the operation specified by the instruction

  • nonprogrammable system

    • control unit is not responsible for obtaining instructions, nor for sequencing the execution of those instructions

    • control unit determines the operation to be performed & the sequence of those operations, based on only its inputs and the status bits


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8-2 Algorithmic State Machines

  • The ASM Chart

    a) state box :- register transfer operations or output signals

    c) decision box :- describes the effect of inputs on the control

    d) conditional ouput box :- from decision box

Figure 8-1 ASM Chart Elements


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8-2 Algorithmic State Machines

  • ASM Block

Figure 8-2

ASM Block


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8-2 Algorithmic State Machines

  • Timing Consideration

Figure 8-3 ASM Timing Behavior


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8-3 ASM Chart Examples

  • introduce a hardware algorithm for binary multiplication,propose a simple datapath for its implementation, & then describe its register transfers and control by use of an ASM

  • multiplies 2 unsigned binary numbers

  • Binary Multiplier

    • a copy of the multiplicand is added to a partial product & the partial product is stored in a register for the shift action

    • the partial product is shifted to the right

      (adder is needed for only n bit

      positions instead of 2n bit)

Figure 8-4

Hand Multiplication Example


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8-3 ASM Chart Examples

  • Multiplication Algorithm

Figure 8-5

Hardware Multiplication Example


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8-3 ASM Chart Examples

  • Multiplicer Block Diagram

Figure 8-6 Block Diagram for Binary Multiplier


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8-3 ASM Chart Examples

  • Multiplier ASM Chart

    • [IDLE]:

      • multiplication process starts when G becomes 1

        (ASM moves from state IDLE to state MUL0)

    • [MUL0]:

      • a decision is made based on Q0

    • [MUL1]:

      • a right shift is performed on C, A, & Q

      • C  0, A(n-1)  C, A  sr A, Q(n-1)  A(0), Q  sr Q

        or C  A  Q  sr C  A  Q

Figure 8-7 ASM Chart for Binary Multiplier


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8-3 ASM Chart Examples

Figure 8-8

Alternative Binary Multiplier


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8-4 Hardwired Control

Table 8-1 Control Signal for Binary Multiplier


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8-4 Hardwired Control

  • Sequencing Part of ASM Chart

    • information on sequencing is represented with information on microoperations removed

    • conditional output boxes are removed

    • decision box not affecting the next state is removed

    • design the sequencing part of the control unit with the ASM chart i.e. the part that represents the next-state behavior

Figure 8-9 Sequencing Part of ASM Chart for the Binary Multiplier


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8-4 Hardwired Control

  • Sequence Register and Decoder

    • provide an output signal corresponding to each of the states

    • A register with n F-Fs can have up to 2n states & n-to-2n decoder has up to 2n outputs, one for each of the states

    • consist of 3 states and 2 inputs

       2 F-Fs and 2-to-4-line decoder

Table 8-2 State Table for Sequence Register and Decoder

Part of Multiplier Control Unit


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8-4 Hardwired Control

  • state table for the sequencing part

    • designate 2 F-Fs as M1 & M0

    • state 00 (IDLE), 01 (MUL0), 10 (MUL1)

  • input equations for F-Fs

    DM0 = IDLE • G + MUL1 • Z' & DM1 = MUL0

Figure 8-10

Control Unit for

Binary Multiplier

Using a Sequence

Register and a Decoder


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8-4 Hardwired Control

  • One Flip-Flip per state

    • another possible method of control logic design

    • a F-F is assigned to each of the state,

      • only one of F-F contains a 1, with others 0

Figure 8-11

Transformation Rules

For Control Unit with

One Flip-Flop per State


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8-4 Hardwired Control

  • Control unit with one flip-flop per state

Figure 8-12

Control Unit with

One Flip-Flop per

State for the Binary

Multiplier


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8-5 HDL Representation of the Binary Multiplier-VHDL

Figure 8-13

VHDL Description of a

Binary Multiplier


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8-5 HDL Representation of the Binary Multiplier-VHDL

Figure 8-14

VHDL Description of a

Binary Multiplier (continued)


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8-6 HDL Representation of the Binary Multiplier-Verilog

Figure 8-15

Verilog Description of a

Binary Multiplier


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8-6 HDL Representation of the Binary Multiplier-Verilog

Figure 8-16

Verilog Description of a

Binary Multiplier(Continued)


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8-7 Microprogrammed Control

  • microprogrammed control

    • a control unit with its binary values stored as words in memory

  • microinstructions

    • one or more microinstructions

  • microprogram

    • fixed at the time of the system design & stored in ROM

Figure 8-17

Microprogrammed Control

Unit Organization


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