Download Lab 2

Laboratory 2: Use of the .EXE File
Type in the following programme using EMU8086 and include your
Name, Class, Group, Year and Date. Save this programme as file:
lab_2.asm.
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TITLE
NAME
DATE
CLASS
GROUP
Purpose of Lab
Introduction to the format of the EXE file.
REQUIREMENTS:
You are required to type in the programme below using EMU8086
Emulator.
SPECIFICATION:
1. Open a new .EXE template in the EMU8086 emulator.
2. Copy the Lab 2 programme below into the relevant segments of the
EMU8086 editor.
3. Assemble and Emulate the programme using the Emulate option
from the menubar.
4. Run the programme using the Single Step option from the
menubar.
5. Examine the contents of the AX register and memory variables
locations for word1, word2 and result.
6. Change the variables for word1 and word2 and repeat steps 1 to 5.
DESIGN:
You are expected to try and understand the flow of the programme.
IMPLEMENTATION:
The 8086 processor uses segmentation. It views a programme as being
divided into segments. Namely code, data and stack segments. Hence,
when you write an 8086 assembly language programme you must define
these segments with special assembler directives: SEGMENT to begin a
segment and ENDS to end a segment. Also we normally don't refer to
specific memory addresses. Instead we use symbolic addresses and
special directives to associate them with 8-bit.16-bit or 32-bit locations:
DB DW and DD. We must tell the assembler what segment registers to
use with what segments. To do this we use the ASSUME directive. We
can label any instruction by preceding the instruction with the label we
wish to use followed by a colon. The colon tells the assembler that the
word preceding it was a label not an instruction. Labels are useful when
we want to jump to a specific instruction during the execution of a
programme loop.
The difference between the .EXE and .COM is that .EXE can have
different segments for data, code and stack but the .COM file always
loads in the lowest available segment and 100h from the start of the
segment. This means all code, data and stack must fit in one 64K
segment.
Hence, programming using the .COM needs more knowledge on the part
of the programmers in the sense that they do not over write other data in
the same segment.
Lab 2 Programme:
;*************************************************************
; Simple Arithmetic
; This programme demonstrates some simple arithmetic instructions.
data_seg segment
word1 dw 1234H
word2 dw 5678H
result dw ?
data_seg ends
stack_seg segment stack
; this segment is called data_seg
; Some type definitions for the variables we will declare:
; here we reserve two l6-bit locations which we can refer to
using the symbolic addresses word and word2.
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; They are initialised to HEX 1234 and 5678.
; this is the end of the segment called data_seg
;a new segment called stack_seg. Because this is specially
used ;for the stack we specify this by following the segment
directive ;with the special stack directive.
block dw 50 dup(?)
;the stack is 50 words long. block is the symbolic address of
the ;first of the fifty locations. The other addresses are
block+1 up ;to block+49.
stack_seg ends
code_seg segment
assume cs:code_seg, ds:data_seg,ss:stack_seg
main: mov ax,data_seg
;programmer must initialize
mov ds, ax
; DS and ES register ;for EXE programmes
mov ax,word1
add ax,word2
mov result,ax
code_seg ends
end main
end
;*************************************************************