Computer Organization - Programming the basic computer : Machine Language, Assembly Language and Assembler

GANDHINAGAR INSTITUTE OF TECHNOLOGY
Computer Engineering Department
Computer Organization(2140707)
Programming the basic computer :
Machine language, Assembly language, Assembler
and passes of assembler.
PREPARED BY:
Maitri Thakkar9150120107064)
GUIDED BY:
Prof. Raxit Jani

INTRODUCTION
 A computer system includes both hardware
and software. The designer should be
familiar with both of them.
 This chapter introduces some basic
programming concepts and shows their
relation to the hardware representation of
instructions.
 A program may be : dependent or
independent on the computer that runs it.

MACHINE LANGUAGE
 Program: A list of instructions that direct the
computer to perform a data processing task.
 There are many programming languages (C++,
JAVA). However, the computer executes programs
when they are represented internally in binary form.
 Categories of Programs:
 Machine Language:
• Binary Code
• Octal or hexadecimal code
 Assembly Language:
• Symbolic code
 High level programming languages

INSTRUCTION SET OF THE BASIC COMPUTER:
Symbol Hex code Description
 AND 0 or 8 AND M to AC
 ADD 1 or 9 Add M to AC, carry to E
 LDA 2 or A Load AC from M
 STA 3 or B Store AC in M
 BUN 4 or C Branch unconditionally to m
 BSA 5 or D Save return address in m and
branch to m+1
 ISZ 6 or E Increment M and skip if zero
 CLA 7800 Clear AC
 CLE 7400 Clear E
 CMA 7200 Complement AC
 CME 7100 Complement E
 CIR 7080 Circulate right E and AC
 CIL 7040 Circulate left E and AC
 INC 7020 Increment AC, carry to E
 SPA 7010 Skip if AC is positive
 SNA 7008 Skip if AC is negative
 SZA 7004 Skip if AC is zero
 SZE 7002 Skip if E is zero
 HLT 7001 Halt computer
 INP F800 Input information and clear
flag
 OUT F400 Output information and clear
flag
 SKI F200 Skip if input flag is on
 SKO F100 Skip if output flag is on
 ION F080 Turn interrupt on
 IOF F040 Turn interrupt off
Here,
m: effective address
M: memory word
(operand) found at
m.

BINARY PROGRAM TO ADD
TWO NUMBERS:
Location Instruction Code
0 0010 0000 0000 0100
1 0001 0000 0000 0101
10 0011 0000 0000 0110
11 0111 0000 0000 0001
100 0000 0000 0101 0011
101 1111 1111 1110 1001
110 0000 0000 0000 0000
HEXADECIMAL PROGRAM
TO ADD TWO NUMBERS:
Location Instruction
000 2004
001 1005
002 3006
003 7001
004 0053
005 FFE9
006 0000
PROGRAM WITH
SYMBOLIC OPCODE:
Location Instruction Comments
000 LDA 004 Load 1st operand into
001 ADD 005 Add 2nd operand to AC
002 STA 006 Store sum in location 0
003 HLT Halt computer
004 0053 1st operand
005 FFE9 2nd operand (negative)
006 0000 Store sum here
FORTRAN PROGRAM:
INTEGER A, B, C
DATA A,83 / B,-23
C = A + B
END

ASSEMBLY LEVEL LANGUAGE
 The symbolic program(contains letters, numerals or
special characters) is referred to as an assembly
language program.
 The basic unit of an assembly language program is
a line of code.
 Each line of assembly language program is
arranged in three columns called fields:
 The label field may be empty or it may contain a
symbolic address of up to 3 characters.
 The instruction field specifies a machine instruction or a
pseudo instruction.
 The comment field may be empty or it may include a
comment.

INSTRUCTION FIELD:
 Instruction field in an assembly level language may
specify one of the following three items:
 A memory-reference instruction(MRI) : MRI consist of
two or three symbols separated by spaces.
 ADD OPR (direct address MRI)
 ADD PTR I (indirect address MRI)
 A register-reference or input-output instruction(Non-
MRI) : Non MRI instructions do not have an address
part.
 Pseudo instruction with or without operand : Symbolic
address used in the instruction field must be defined
somewhere as a label.

PSEUDO INSTRUCTION:
 Pseudo instruction is not a machine instruction but
rather an instruction to the assembler giving
information about some phase of translation.
 Four pseudo instructions that are recognized by an
assembler are:
 ORG N : Hexadecimal number N is the memory loc. for
the instruction or operand listed in the following line.
 END : Denotes the end of symbolic program.
 DEC N : Signed decimal number N to be converted to
binary.
 HEX N : Hexadecimal number N to be converted to
binary.

ASSEMBLER:
 An assembler is a program that accepts a symbolic
language program and produces its binary machine
language equivalent.
 The input symbolic program is called the source
program and the output binary program is called the
output program.
 The assembler is a program that operates on
character strings and produces an equivalent binary
interpretation.

FIRST PASS OF AN ASSEMBLER:
 During the first pass, the assembler
generates a table that corelates all user-
defined address symbols with their binary
equivalent value.
LC := 0
Scan next line of code Set LC
Label
no
yes
yes
no
ORG
Store symbol
in address-
symbol table
together with
value of LC
END
Increment LC
Go to
second
pass
no
yes

SECOND PASS :
Second pass
LC <- 0
Scan next line of code
Set LC
yes
yes
ORGPseudo
instr.
yes
END
no
Done
yes
MRI
no
Valid
non-MRI
instr.
no
Convert
operand
to binary
and store
in location
given by LC
no
DEC or
HEX
Error in
line of
code
Store binary
equivalent of
instruction
in location
given by LC
yes
no
Get operation code
and set bits 2-4
Search address-
symbol table for
binary equivalent
of symbol address
and set bits 5-16
I
Set
first
bit to 0
Set
first
bit to 1
yes no
Assemble all parts of
binary instruction and
store in location given by LC
Increment LC
The binary
Translation is
done during the
second pass.

Computer Organization - Programming the basic computer : Machine Language, Assembly Language and Assembler

Computer Organization - Programming the basic computer : Machine Language, Assembly Language and Assembler

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