Instruction Types


Instruction Types:

Instruction from the memory is read into the instruction register whose format is:

15                                                                                                                                                                              0

Instruction Register

The format of the instruction is shown below:

Mode Bit (M)

OPCODE

Address

15

14 13 12

11———————– 0

The Instruction types are:

Mode Bit (M)

OPCODE

Hex Code

Instruction Number

Instruction

Address

15

14 – 12

Hex

Direct Memory

16-Bit Format

Hex

11———————– 0

0

000

001

010

011

100

101

110

D0 Add

D1 AND

D2 SUB

D3 XOR

D4 OR

D5

D6

0XXX

1XXX

2XXX

3XXX

4XXX

5XXX

6XXX

Direct memory Instruction

Bit 11—0 represent the reference to data operands.

1

1

000

001

010

011

100

101

110

8 Add

9

A

B

C

D

E

8XXX

9XXX

AXXX

BXXX

CXXX

DXXX

EXXX

Indirect memory reference Instruction

0

111

D7

7XXX

Register type instruction. The bit 11 – 0 represent different register type operations

CLA

CLE

STC

CLC

1

111

F I/O

FXXX

With Mode bit=1 and Opcode bits=111 represent I/O type instruction

IN

OUT

Type

1. Direct memory reference instruction (M=0, (14-12) D0 —D6

2. InDirect memory reference instruction (M=1, (14-12) D0 —D6

3. Register Type (M=0, (14-12) – 111 (D7)

4 I/O Type of Instruction (M=1, (14-12) 111

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