Lecture 20

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Lecture 20

  1. 1. Control Unit 1 Lecture 20 CSE 211, Computer Organization and Architecture Harjeet Kaur, CSE/IT Overview  Control Memory  Comparison of Implementations Sequencing Microinstructions Design of Control Unit  Address Sequencer
  2. 2. Basic Computer Orgsnization and Design 2 Lecture 20 CSE 211, Computer Organization and Architecture Harjeet Kaur, CSE/IT Control Unit  Control unit (CU) of a processor translates from machine instructions to the control signals for the microoperations that implement them  Control units are implemented in one of two ways Hardwired Control CU is made up of sequential and combinational circuits to generate the control signals Microprogrammed Control A control memory on the processor contains microprograms that activate the necessary control signals
  3. 3. Control Unit 3 Lecture 20 CSE 211, Computer Organization and Architecture Harjeet Kaur, CSE/IT Control Unit Implementations Combinational Logic Circuits (Hard-wired) Microprogram I R Status F/Fs Control Data Combinational Logic Circuits Control Points CPU Memory Timing State Ins. Cycle State Control Unit's State Status F/Fs Control Data Next Address Generation Logic C S A R Control Storage (-program memory) M e m o r y I R C S D R C P s CPUD }
  4. 4. Control Unit 4 Lecture 20 CSE 211, Computer Organization and Architecture Harjeet Kaur, CSE/IT Terminology Microprogram - Program stored in memory that generates all the control signals required to execute the instruction set correctly - Consists of microinstructions Microinstruction - Contains a control word and a sequencing word Control Word - All the control information required for one clock cycle Sequencing Word - Information needed to decide the next microinstruction address - Vocabulary to write a microprogram Control Memory(Control Storage: CS) - Storage in the microprogrammed control unit to store the microprogram Writeable Control Memory(Writeable Control Storage:WCS) - CS whose contents can be modified -> Allows the microprogram can be changed -> Instruction set can be changed or modified Dynamic Microprogramming - Computer system whose control unit is implemented with a microprogram in WCS - Microprogram can be changed by a systems programmer or a user
  5. 5. Control Unit 5 Lecture 20 CSE 211, Computer Organization and Architecture Harjeet Kaur, CSE/IT Terminology Sequencer (Microprogram Sequencer) A Microprogram Control Unit that determines the Microinstruction Address to be executed in the next clock cycle - In-line Sequencing - Branch - Conditional Branch - Subroutine - Loop - Instruction OP-code mapping

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