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Computer Organization
Instructors :
Dr. Abdul Raouf Khan
Mr.Marwan El-Haj
Computer Instructions
The following type of instructions must be
included in a computer
1. Arithmetic, logical and shift instructions
2. Instructions for moving information ( data transfer)
to and from memory & processor register.
3. Program Control instructions together with
instructions that check status conditions
4. Input & output instructions

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Basic Computer Instruction
Formats
Basic Computer Instruction
Formats Contd
Memory reference instructions, uses 12 bits to
specify the address mode I. I=0 for direct address
and I= 1 for indirect address

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Basic Computer Instruction
Formats Contd
The register reference instruction are recognized by
the opcode 111 , with a 0 in the left most bit (bit 15)
of the instruction. A register reference instruction
specifies an operation on or a test of the AC register.
An operand from memory is not needed, therefore,
the other bits are used to specify the operation or
test to be executed.
Basic Computer Instruction
Formats Contd
Similarly, an input – output instruction does
not need a reference to memory and is
recognized by the opcode 111 with a 1 in the
bit position 15. the remaining 12 bits are
used to specify the type of input- output
operation or test to be performed.

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Memory Reference Instructions
Register Reference Instructions

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Input – output Instructions