1991-03-16 — Page 25

肉汁

( 25 )育教 日一初月二年未辛膺夏

報日憍

六期星 日六十月三(一九九一)年十八國民華中

Computer(24)

Example: write machine codes for the following machine instruction

using the operation codes just defined.

(a)Move the content of memory location 15 to the accumulator.

100.01111

Central Memory

Memory

Content

location

1991 中學會考預習專欄

明德出版社

MILL & DALE PRESS

K. Choy

LOAD Operand

Of111z - 15:0

1

10001111

00010000

10110001

Computer Operation by Machine Code.

Machine code is machine dependent, different machines use different machine codes. Therefore questions of computer operation will assume a list of operation code:

Basic assumptions

(1)The computer uses 8-bit words to represent instruction.

(Memory location 15)

(b)Add the content of memory location 15 to the accumulator..

01100000

11100000

000,10000

ADD Operand

10000元=

1610

Memory locations not used.

00001001

Machine code program stored in the memory location

訊航 E

周赕慈利 自從印尼 後,由本港到 有若干本港旅 由五天虿九天 因多蘭旅行瑚 應可能不去,

E

巴 點美

未必会

!

溷遊⌈ 千元:

(memory Jocation 16)

.00001010

Datd stored in the memory.locations.

00010011

(c)store the content of accumulator to the memory location 17.

101 10001

Memory locations not used.

STORE. Operand

10001 = 17

3 bits Queration

code

5. bits Operand

The first 3 wits are the operation codes and the last 5 bits are use to represent the operands.

(2)3 bits of operation codes can stand for B different instructions. (3)5 bits of operand can stand for 2 operands i.e. 32 memory!

locations.

(4)A set of operation codes are used for explanation. It is necessary to realize that the table will be different from thosej defined in the examination paper. Therefore you are suggested to Tearn only the idea.

Type of

Operation

Operation

Code

Arithmetic Operation

000

Input/output operation

.001

011

Moving data

100.

Sequence

110

. control

Program control

Operation description

ADD the content of the memory location (operand) to the content of accumulator. The result is stored in the accumulator,

SUBTRACT the content of the operand from the content of the accumulator. The result is stored in the accumulator.

INPUT a number from the keyboard and store the value into the accumulator.

OUTPUT the content of the

·accumulator to the monitor screen.

LOAD the content of the operand into the accumulator.

STORE the content of the

accumulator into the memory

specified by the operand.

JUMP to the locationfeet f

秘

the operand if the fontie

accumulator is less a

STOP program execution.

(memory location 17)

(d)Display the content of the accumulator to the monitor screen.

011 00000

OUTPUT Neglected because the monitor screen is assumed.. (e)urite a machine code program to add two numbers stored in memory

focations:15 and 17. The sum is then stored in location 17. The result is displayed on the monitor screen.

Flowchart

START

Machine code program,

Program 010-00000

101 10000

Move the, content

010 00000

of Tocation 15

to ACC

101 01111

100-01111

000 10000

000 10000

101, 10001

01:1 :00000

101 10001

Add the content

of location 16

to the ACC

Store the content

of ACC to

location 17

sp the

content of ACC,

to ine 'screen

STOP

011.00000

111 00000

圖

*Remarks: The program and the data are both stored in the memory

locations. The storage is shown below:

Operation code

000

001

010

011

100"

101

110

1.11

The last machine program may be changed to assembly language:"

Assembly language

*IMP

STA 16

INP

T 01111.

000 10000

101 10001

011 00000

411 00000

STA 15

ADD. .16

STA

17

OUP

"STP

Program dry run

Instruction

·Accumulator

15

16

17

Screen

1.0

10

19.

10

19

10

19

10

19

$

Example: Modify the program so that the two values should be input

through the keyboard.

111 00000

Explanation

Input a value through keyboard. Store the value to location 16. Input the second value.

Store the value to location 15. Add location 16 to accumulator. Store the 'sum to location 1.7. Display the sum

. Stop:program execution.

Assembly Language.

Machine codes are difficult to handle.

-Mnemonic codes are used to represent the operation codes. In

recent papers, mnemonic codes are used for machine codes.

Mnemonic codes should be changed to machine codes before it can be ̇executed by the translation program called the assembler. Example:

Mnemonic code

ADD

SUB

INP

OUP

LOA

STA

JMP

STP

ent assemblers for different machines use different mnemonic les.

5

預

倒

五千

詢相

印尼旅遊業漸蓬勃

旅行團行程有出入

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·的航空貨運中心,特別是有中國

由 - 認爲本港在亞洲區是具實質 華民航空是次申請所持之理

采月矛耳言證明不裕言

公司指出,確能配合下一個世紀 至於香港新機場的興趣,該 的航空貨運發展,而現時國泰航

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