Instruction Formats in Computer Architecture
Instruction
formats
What
is
instruction
format?
•
An
instruction
is normally
made up
of
a
combination
of an
operation code
and
some way of specifying an
operand
,
most
commonly
by
its
location or
address
in
memory
Types
of
address
instructions
Three address instructions
•
Memory
addresses for the
two
operands and
one destination need to be specified.
•
It
is
also called
General
register
organization
.
•
I
n
s
t
r
u
c
t
i
o
n
:
A
D
D
R
1
,
R
2
,
R
3
M
i
c
r
o
o
p
e
r
a
t
i
o
n
:
R
1
R
2
+
R
3
EVALUATE
X=(A+B)*(C+D)
X=A+(B.C)+(D.E)
Two address
instructions
•
Two
address registers or
two memory
locations are
specified
•
Assumes
that the destination address is the
same
as that of the first
operand
.
•
I
n
s
t
r
u
c
t
i
o
n
:
A
D
D
R
1
,
R
2
M
i
c
r
o
o
p
e
r
a
t
i
o
n
:
R
1
R
1
+
R
2
EVALUATE
X=(A+B)*(C+D)
X=A+(B.C)+(D.E)
One address
instructions
•
One address can be a register name or
memory
address.
•
S
I
N
G
L
E
A
C
C
U
M
U
L
A
T
O
R
O
R
G
A
N
I
Z
A
T
I
O
N
•
It
uses AC register for all
data
manipulation
•
I
n
s
t
r
u
c
t
i
o
n
:
A
D
D
X
M
i
c
r
o
o
p
e
r
a
t
i
o
n
:
A
C
A
C
+
M
[
X
]
EVALUATE
X=(A+B)*(C+D)
X=A+(B.C)+(D.E)
Zero address
instruction
•
Stack
is used.
Arithmetic
operation pops
two
operands from
the stack and pushes the
result.
•
A
l
s
o
c
a
l
l
e
d
s
t
a
c
k
o
r
g
a
n
i
z
a
t
i
o
n
Zero address
instruction
•
E
v
a
l
u
a
t
e
X
=
(
A
+
B
)
*
(
C
+
D
)
Addressing
Modes
Addressing
mode
specifies a rule for
interpreting or
modifying
the
address field
of the instruction
before
the operand
is
actually
executed.
Well
known addressing
modes-
•
•
•
•
•
•
•
•
•
•
Implied mode
Immediate mode
Register mode
Register indirect
mode
Autoincrement or
Autodecrement
D
i
r
e
c
t
a
d
d
r
e
s
s
m
o
d
e
I
n
d
i
r
e
c
t
a
d
d
r
e
s
s
m
o
d
e
R
e
l
a
t
i
v
e
a
d
d
r
e
s
s
m
o
d
e
I
n
d
e
x
e
d
a
d
d
r
e
s
s
i
n
g
m
o
d
e
Base register addressing
mode
Implied
Mode
•
In
this mode
the operands are specified
implicitly
in the
definition
of the
instruction.
•
All
register reference instructions that use an
accumulator are
implied mode
instruction.
•
Example: CMA compliment
accumulator.
Immediate
Addressing
•
Data
needed
by
the processor is contained
in
the
instruction
•
Operand=
address
field
•
e.g-ADD
5
-add 5 to the content of
accumulator
-5
is
the
operand
opcode
Operand
(5)
Register
Addressing
•
Operand
is held
in register named in address
field
A
k-bit field can specify
any
one
of
2^k
registers
•
R
E
G
I
S
T
E
R
S
Register Indirect
Addressing
•
The
selected register contains
the
address
of
the
operand
rather than
the
operand
itself.
Mem
o
ry
50
0
Auto Increment or
Auto Decrement
Mode
•
This
is similar
to the
register indirect mode except
that the register is
incremented
or
decremented
after or before
its value is used
to
access
memory
.
R1=400
399
40
0
1.
Auto
incr-E.A=400
R1
is
incremented
to 401after the
execution
2.
Auto
decr-R1
is
decremented prior
to the
execution,therefore,R1=399 and
E.A=399
RELATIVE ADDRESS
MODE
•
In
this mode the content of the program
counter is
added
to the
address part
of
the
instruction
to
obtain
the effective
address.
2
4
MEMO
R
Y
826
+
Effective
850
Address
826+24
Indexed
addressing
mode
•
In
this mode the content of an index register is
added
to
the address part of
the
instruction
to
obtain
the effective
address.
opcode
Rb
Rt
ADDRESS(20)
index
register(1000)
+
1
020
E.A
10
00
2
0
Mem
o
r
y
BASE REGISTER ADDRESSING MODE
•
In
this mode the content of
a
base register is
added
to the
address part of
the
instruction
to
obtain the
effective
address.
opcode
Rb
Rt
ADDRESS
REGISTER(400)
Mem
o
ry
10
0
400
+
50
0
E.A
Explore different types of instruction formats in computer architecture, including one-address, two-address, and zero-address instructions. Learn how instructions are structured and executed, such as specifying operands and memory addresses. Dive into examples like evaluating expressions and organizing data manipulation with various addressing schemes.
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Presentation Transcript
What is instructionformat? An instruction is normally made up of a combination of an operation code and some way of specifying an operand, most commonly by its location or address in memory
Types of address instructions Three address instructions Memory addresses for the two operands and one destination need to be specified. It is also called General register organization. Instruction: ADD R1, R2, R3 Microoperation: R1 R2 +R3
EVALUATE X=(A+B)*(C+D) ADD ADD MUL R1, A, B R2, C, D X, R1, R2 R1 M[A]+M[B] R2 M[C]+M[D] M[X] R1*R2 X=A+(B.C)+(D.E)
Two addressinstructions Two address registers or two memory locations are specified Assumes that the destination address is the same as that of the first operand. Instruction: ADD R1, R2 Microoperation: R1 R1 +R2
EVALUATE X=(A+B)*(C+D) MOV ADD MOV ADD MUL MOV R1, A R1, B R2, C R2, D R1,R2 X,R1 R1 M[A] R1 R1+M[B] R2 M[C] R2 R2+M[D] R1 R1*R2 M[X] R1 X=A+(B.C)+(D.E)
One addressinstructions One address can be a register name or memory address. SINGLE ACCUMULATOR ORGANIZATION It uses AC register for all data manipulation Instruction: ADD X Microoperation: AC AC + M[X]
EVALUATE X=(A+B)*(C+D) LOAD ADD STORE LOAD ADD MUL STORE A B T C D T X AC M[A] AC AC+M[B] M[T] AC AC M[C] AC AC+M[D] AC AC*M[T] M[X] AC X=A+(B.C)+(D.E)
Zero addressinstruction Stack is used. Arithmetic operation pops two operands from the stack and pushes the result. Also called stack organization
Zero address instruction Evaluate X = ( A +B ) * ( C +D ) PUSH A PUSH ADD TOS A TOS B TOS (A+B) Push A Push B ADD Push C Push D ADD Mult Store B TOS C PUSH C TOS D PUSH D TOS (C+D) TOS (C+D)*(A+B) M[X] TOS ADD MUL POP X
Addressing Modes Addressing mode specifies a rule for interpreting or modifying the address field of the instruction before the operand is actually executed.
Well known addressing modes- Implied mode Immediate mode Register mode Register indirect mode Autoincrement or Autodecrement Direct address mode Indirect address mode Relative address mode Indexed addressing mode Base register addressing mode
Implied Mode In this mode the operands are specified implicitly in the definition of the instruction. All register reference instructions that use an accumulator are implied mode instruction. Example: CMA compliment accumulator.
Immediate Addressing Data needed by the processor is contained in the instruction Operand= address field e.g-ADD 5 -add 5 to the content of accumulator -5 is the operand opcode Operand (5)
Register Addressing Operand is held in register named in address field A k-bit field can specify any one of 2^k registers REGISTERS OPCODE REGISTER ADDRESS R OPERAND
Register Indirect Addressing The selected register contains the address of the operand rather than the operand itself. REGISTER ADDRESS R OPCODE 500 REGISTERS OPERAND(72) R ADDRESS OF OPERAND(500) Memory
Auto Increment orAuto Decrement Mode This is similar to the register indirect mode except that the register is incremented or decremented after or before its value is used to access memory. R1=400 1. Auto incr-E.A=400 R1 is incremented to 401after the execution 450 700 399 400 2. Auto decr-R1 is decremented prior to the execution,therefore,R1=399 and E.A=399
RELATIVE ADDRESSMODE In this mode the content of the program counter is added to the address part of the instruction to obtain the effective address. Address(24) OPCODE MEMORY PC (825) 24 Effective850 826 + Address 826+24
Indexed addressingmode In this mode the content of an index register is added to the address part of the instruction to obtain the effective address. opcode Rb Rt ADDRESS(20) 20 index register(1000) Memory E.A 1000 + operand 1020
BASE REGISTER ADDRESSING MODE In this mode the content of a base register is added to the address part of the instruction to obtain the effective address. opcode Rb Rt ADDRESS REGISTER(400) Memory 100 400 + 500 42 E.A
