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ch07 - Chap.(ControlUnit s 71 7-1 Control Memory Control...

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Computer System Architecture Dept. of Info. Of Computer Chap. 7 Microprogrammed Control Chap. 7 7-1 Chap. 7  Microprogrammed Control (Control Unit) 7-1 Control Memory Control Unit Initiate sequences of microoperations » Control signal ( that specify microoperations ) in a bus-organized system groups of bits that select the paths in multiplexers, decoders, and arithmetic logic units Two major types of Control Unit » Hardwired Control : in Chap. 5 The control logic is implemented with gates, F/Fs, decoders, and other digital circuits + Fast operation, - Wiring change(if the design has to be modified) » Microprogrammed Control : in this Chapter The control information is stored in a control memory, and the control memory is programmed to initiate the required sequence of microoperations + Any required change can be done by updating the microprogram in control memory, - Slow operation Control Word The control variables at any given time can be represented by a string of 1’s and 0’s. Microprogrammed Control Unit A control unit whose binary control variables are stored in memory ( control memory ).
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Computer System Architecture Dept. of Info. Of Computer Chap. 7 Microprogrammed Control Chap. 7 7-2 Microinstruction : Control Word in Control Memory The microinstruction specifies one or more microoperations Microprogram A sequence of microinstruction » Dynamic microprogramming : Control Memory = RAM RAM can be used for writing ( to change a writable control memory ) Microprogram is loaded initially from an auxiliary memory such as a magnetic disk » Static microprogramming : Control Memory = ROM Control words in ROM are made permanent during the hardware production. Microprogrammed control Organization : Fig. 7-1 1) Control Memory » A memory is part of a control unit : Microprogram » Computer Memory ( employs a microprogrammed control unit ) Main Memory : for storing user program ( Machine instruction/data ) Control Memory : for storing microprogram ( Microinstruction ) 2) Control Address Register » Specify the address of the microinstruction 3) Sequencer (= Next Address Generator ) » Determine the address sequence that is read from control memory » Next address of the next microinstruction can be specified several way depending on the sequencer input : p. 217, [1, 2, 3, and 4] User Program Machine Instruction Microprogram Microinstruction Microoperation
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Computer System Architecture Dept. of Info. Of Computer Chap. 7 Microprogrammed Control Chap. 7 7-3 4) Control Data Register (= Pipeline Register ) » Hold the microinstruction read from control memory » Allows the execution of the microoperations specified by the control word simultaneously with the generation of the next microinstruction RISC Architecture Concept RISC(Reduced Instruction Set Computer) system use hardwired control rather than microprogrammed control : Sec. 8-8 7-2 Address Sequencing Address Sequencing = Sequencer : Next Address Generator
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