How does assembly generally begin, and what does the beginning of the assembly code mean?

First define the segment registers used, such as ds, es (can be without) must define ** segment for example: code:segmentassume:cs:code

start: The program to be written.

code ends

end start

org 0030h

start: setb

here: mov p0,#3fh

mov p2,#3fh

mov r0,#00h

mov r1,#00h

mov dptr,#tab

l1: jb ,$

jnb ,$

inc r0

mov a,r0

movc a,@a dptr

mov p2,a

cjne r0,#0ah,l1

l2: inc r1

cjne r1,#0ah,here ;Remove this one.

mov r0,#00h

mov p2,#3fh ;Add this article.

mov a,r1

movc a,@a dptr

mov p0,a

cjne r1,#0ah,l1 ;Add this article.

ajmp here

tab: db 3fh,06h,5bh,4fh,66h,6dh,7dh,07h,7fh,6fh

endbtw：

It is generally better to write this at the beginning of the program.

org 00h

ajmp start

org 30h

segment

db/dwends

assume

These are pseudo-directives, see the relevant information for their purpose and usage. Then you can understand!

Write a program, to segment it.

Data Segment This is a segment ......Data Ends Stack Segment This is another segment ......stack ends code segment This is another segment .........

Write out a few.

Ten or hundreds of segments are fine.

However, when working on a computer, currently, only four segments can be used.

Other segments, idle.

assume cs:code,ds:data,ss:stack,es:data specifies the current segment.

int0:0003h

t0: 000bh

int1:0013h

t1: 001bh

Serial port: 0023h

Generally, a jump command ljmp is written at the corresponding interrupt entry location, and a return instruction reti is written at the end of the interrupt service program

1) What does the $- in $string mean?

A: The $-string represents a continuous storage unit in memory, and $ represents a fixed prefix!

2)dw ?Medium'？'What does that mean?

Answer: DW is used to define words, here? It is used to reserve storage space and does not store any data.

Dear, remember to adopt it.

1) $ represents the current sweatshirt, as in your example, as follows:

dseg segment

string db 'xx..'

length equ $-string

key_addr dw ?

dseg ends

where length=2-0=2, that is, the current offset $ is 2, and the offset of string is 0

2)dw ?Medium'？'Indicates the allocation of 1 word unit (2 bytes) of memory space, the content of the word unit is not initialized, and its value is random, that is, it is not a definite value.

This is because identifiers such as variable names and statement numbers are required to start with a letter.

If you don't add 0, you write abh, and no one can figure out whether this is the hexadecimal number abh or the name of a variable called abh.

We know that hexadecimal data greater than 9fffh a000h, a001h...fffeh, ffffh, etc., all start with a letter when they are written. In assemblers, data can't start with a letter, so 0 should be added in front.

For example, 9138h can be written as "9138h" in the assembly source program, while a000h can be written as "0a000h" in the assembly source program.

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