Design of Microprogrammed Control CPU with I$/$O Interface

Introduction

The goal of this project is to learn the computer architecture with a microprogrammed$-$based CPU, and its connection input$-$output interface $($I$/$O interface$)$ module that can handle simple input and output devices, such as switches and LEDs. The architecture is similar to those described in the textbook $($Computer System Architecture, $3$rd Edition, by M$.$ Morris Mano, Prentice$-$Hall, ISBN: $0-13-175738-5).$ The project activities will focus on implementing and simulating the data unit and the control unit of a CPU, as well as an I$/$O interface module and its connections to the CPU. LogiSim will be used as a designing and simulation tool.

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The proposed architecture, as will be detailed later, is similar to the architecture described in chapter $7,$ with some modifications regarding the supported instruction set, microoperations, and microinstructions format. Moreover, the architecture has some additional registers $($such as INPR and OUTR$)$ and flags $($such as S$,$ N$,$ FGI, and FGO$).$

Description

The purpose of the data unit is to read the words stored in the memory RAM and extract status signals such as the opcode, address and flags listed below and send them to the control unit. In addition, it also executes the control signals received from the control unit such as register load, memory read$/$write and arithmetic, logic and shift unit $($ALU$)$ operations. The Data Unit will send to the Control unit the status signals which include the machine instructions bits which have the $($opcode$,$ indirect bit $,$ address bits and the status flags $($Z$,$I,N$,$S$,$K$,$M$).$ ROM can be used for control memory. The Control Unit will receive the status signals and will produce the sequences of the control signals the control unit will decode the microinstructions into microoperations and will send it to the Data Unit.

The Data Unit works as a medium between the I$/$O interface and the Control Unit; The I$/$O is only connected to the Data Unit. The Control Unit does not have direct access to the I$/$O interface, it gets the I$/$O information from the Data Unit. The Control Unit will produce all the desired control signals which correspond to different microoperations that need to be executed using the status signals $($address bits, opcode, flags$)$ which are provided via the connection between the Control Unit and Data Unit$\mathrm{.}1)$ Task $2$: Complete microprogram routines for all of the instructions in the provided instruction set, using the provided tables of available microinstructions, condition types $($CD$),$ and branch type $($BR$)($see Appendix$).$