s

1. 10/26/2014
1
Computer Organization
Instructors :
Dr. Abdul Raouf Khan
Mr.Marwan El-Haj
Basic Computer Organization and
Design
:Program: It is a set of instructions, that specify
the sequence by which processing has to
occur.
Instruction code: Is a group of bits that instruct
the computer to perform a specific operation.
It is divided into two parts:
a) Operation code b) Operand

2. 10/26/2014
2
Operation code:
The operation code (op code) is a group of
bits that define the operation to be performed
e.g. ADD, SUB, MUL, XOR, etc
The op code has at least ‘n’ bits for a given
2n (or less) distinct operations.
Operand
The operand is the data on which action is to
be performed
e. g
ADD B
Mov x
Etc

3. 10/26/2014
3
Stored Program Organization
Addressing
1. Immediate addressing: when the second
part of the an instruction code specifies an
operand, the instruction is said to have an
immediate operand
2. Direct addressing: when the second part of
an instruction code specifies the address of
an instruction

4. 10/26/2014
4
Addressing contd
3. Indirect addressing: when the second part of
an instruction code specifies the address of a
memory word in which the address of an
operand is found, the instruction is said to
have an indirect address.
Instruction format

5. 10/26/2014
5
Computer Registers
The computer needs processor registers for
manipulating data and a register for holding
address.
The following are the registers needed for a
basic computer and there functions are listed
as well
Computer Registers

6. 10/26/2014
6
Computer Registers

7. 10/26/2014
7
Data transfer
Bus register / memory
From Memory to Bus Read Control of
Memory Should be 1
S2 S1 S0 Decimal equivalent Register
0 0 1 1 AR
0 1 0 2 PC
0 1 1 3 DR
1 0 0 4 AC
1 0 1 5 IR
1 1 0 6 TR
1 1 1 7 Memory
Data transfer
From bus to register
Register bus , load input LD = 1
From bus to memory
Write input WR = 1

8. 10/26/2014
8
Question?
Can We Swap the Contents of two registers
in one Cycle? Explain