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Computer Organization

Instructors :

Dr. Abdul Raouf Khan

Mr.Marwan El-Haj

Last Lecture

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Determine the type of Instruction

� The three instruction types are subdivided

into four separate paths

� D’7IT3 : AR� M[AR]

� D’7I’T3 : Nothing

� D7I’T3 : Execute register-reference Instruction

� D7IT3 : Execute Input-Output instruction

Last Lecture

Register Reference Instructions

� The control function and Microoperation for

register reference are listed below. These

instructions are executed with the clock

transition associated with timing Variable T3.

� Each control function needs the Boolean

relation D7I’ T3, which we designate by r.

� The control function is distinguished by one

of the bits in IR(0-11)

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Register Reference Instructions

Memory Reference Instructions

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Memory Reference Instructions

Memory Reference InstructionsExample of BSA Instruction

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Input Output Configuration

Input process

� Initially input flag FGI is cleared to 0. When a

key is struck in the keyboard, an 8 bit

character is shifted into INPR and FGI is set

1. As long as the flag is set, the information

in INPR cannot be changed. The computer

checks the flag bit; if it is 1, the information

from INPR is transferred in parallel into AC

and FGI is cleared to 0.

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Output process

� Initially, the FGO = 1. the computer checks the

flag bit; if it is 1, the information from AC is

transferred in parallel to OUTR and FGO is

cleared to 0. the output device accepts the

coded information, prints the character and

when the operation is completed, sets FGO = 1.

Computer does not load new character in

OUTR if FGO = 0.

Input-Output instructions

� For all input-output instructions, D7=1, I=1

and T3=1. Each control function needs a

Boolean relation D7IT3 = p (say)

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Input-Output instructions