Optron #20 25 октября 1998

Программирование

Premiere headings - New Topic "Likbez - Assembler: a view from afar.

Hacker Rasp


  On the anniversary of "OPTRON" We timed the premiere of a new 
column - "literacy campaign". It will published a variety of 
"educational" materials on soft, hard, etc. 

  Of course, this topic - is not an invention of our editorial 
staff. Such published Deja Vu, Proton, Aspect and many others

electronic publications.

  A "Plutonium" from the very first issue contains a section 
with the same as that us, the name (though in "Plutoniume" she

not so much "education" as
"Journalistic" and purely "educational" materials are placed 
outside this column).


  So "Optron" just to be a common example.

  Of course, we can say: "You what,
so lazy that you are going to fill the volume of newspaper 
rewritten reference materials? But at the same time deprive the 
user joy of self-search, to wean

to use workbooks and textbooks? "

  But we do not intend to do so!

  "Formerly known information" will be placed in the 
"Optocouplers" only in cases when it:


  - For one reason or another unavailable
readers of the newspaper;

  - Was scattered on different sources and
shows the author in a system;

  - Regarded by the author with his
own particular point of view.

  In short, the motto of our new column will: a special look at 
the well-known. 

  Opens the Field series of articles on Assembler. Infarh, the 
author of this series, the sign Readers' Optron "as the lead

"Litstranichki. But this time it appears in the new incarnation.

  "Infarh excellent command of words, knows the needs and 
concerns of our users - reasoned editorial. - So who else but

him to be a guru? "Therefore, since this
release, Infarh addition to concerns about
"Litstranichke" shoulder to shoulder
More and Likbez. So wish him luck
in this endeavor!



        Assembler: a view from afar

Infarh, 1998


                Entry


  Greetings, dear readers
Optocoupler! Today on your numerous
applications we begin a series of articles that
is an assembler and what it eats. " A
"Eat" it, I should say, first with a headache, and then with 
pleasure. 

  In fact, not in vain because the assembler is the main 
programming language on Speccy. None of the other languages 
​​(BASIC, Pascal, C, ...) does not give a tenth of

opportunities assembler. Program in assembly language much 
faster, takes up less space in memory and provides programmer 
is much more room for "Bullying" over the machine.


  To begin with I want to warn that this
the story is designed for those with speech
"Number system" does not cause an irresistible urge to kick 
your feet the corpse of a mathematics teacher. And I guess you 
already familiar with the "Basic". It is difficult to start 
from the beginning: always turns out that there was something 
to that. So, we turn to an acquaintance. 



          What is a computer code


  Z80 processor receives signals from the bus
Data (SM) and arranged in such a way that
Different combinations of these signals require that the 
processor to perform one or different function. State line SM

usually described in binary form: "1" -
there is a signal, "0" - no signal. Typical
machine language command might look
as follows:


                001111000


  I think this is somewhat different from the familiar to 
"Basic" 


                LET A = A +1


  Nevertheless, the essence of this command is
follows. That is the machine code. All
the necessary combination of ones and zeros, with
by which management
processor, previously housed in
computer memory.

  I must say that the program in codes
has its drawbacks:


  1) They are difficult to read and debug;

  2) They are longer in the team;

  3) It is difficult to perform arithmetic
action.


  Apparently, some readers have already pulled
hand to the forty-first button with the idea
that this language - only for high-risk
maniacs able to enter into the computer
tens of thousands of combinations of units
and zeros, subject knowledge by heart all
their appointments.

  And here you are absolutely right. Rare fanatic can do in 
such circumstances. More than normal people use ASSEMBLER. 



             The essence of the assembly


  Assembly language was invented just
to not try to understand the meaning of
programs like


                00100001

                00000000

                01000000

etc. Fortunately, for each such combination is possible to 
choose a name that can be read and understood. Such names are 
called mnemonics. For example, at this stage, learning 
construction type



                 INC A

you may not understand, but at least
read. And if you say that the INC -
standard abbreviation of the word INCREMENT
(Sequential increase / increment;
modification of the summation), and "A" - a variable, then you 
will already have some idea of ​​what's happening. Anyway

case, "INC A" certainly more understandable,
than "00111100".

  Between assembly language and machine code
There is only one difference: the assembler to
one level above machine language. Person to read it more easily 
than native code, but On the other hand, the computer can not 
read the language assembler.


  It is not an adaptation of a machine language like "Basic", 
where each operation must be doing a lot of processor commands. 
In assemlere each team corresponds to identical purpose machine 
language command. 

  To write a program to
assembly and bring it into a form understandable
your Speccy, (ie machine code), there are special programs which
further and will be discussed.



           Editors and monitors


  Editor Assembler (hereinafter - just
"Assembler") is a program with which you can enter your computer
program code in assembly language and compile this program into 
machine code, "clear" the processor. That is how the team "INC 
A" transformed into "00111100". 

  At present, there are many editors assembly, both for 48K 
machines, and to 128K. You are faced with having to choose from

them one that is more suitable.

  Now for the monitors. This word means
some kind of program, whose purpose - to help you observe what 
is happening in the computer memory during the execution of 
your (and not just yours) program. About They will be discussed 
in more detail later. 

  And now I'll try to help you choose
The assembler itself, which you'll use and in the future. I 
recommend to take this subject carefully, as each Assemler 
stores program code in its unique format. Wrap text in your 
program (source code) from one editor to another is sometimes 
paired with great difficulties, and success is not always

guaranteed. Changing the assembler, you risk
lose all your previous work.



              What do we have?


  To start recall the memory of your Speccy. True, now there 
are already very few 48-x machines, but still ... For

those - assemblers are much smaller. In
this case, a rare unanimity.
Almost all recommend ispolzobat package
"DEVPAC", which includes assembler "Gens" and
a monitor program "Mons". This combination (assembler and 
monitor in a "one bottle") provides maximum comfort. "Mons", 
everything else can disassemble the program into machine code, 
turning it into a source code format Assembler "Gens". I have 
been using "DEVPAC" - and no complaints about his work is not

had. However, things were so
just before I got
Speccy-128.

  Here - very differently. Assemblers are
many, and your choice I did not at once. List some say a few 
words about each.



                  TASM


  This editor from version to version improved, so the format 
of the text version 2 is not compatible with later. Beginning 
with Version 3, has a function "Import 2.0"

for format conversion. Version 4.0
incorporates a monitor "STS". Assembler is not bad, but 
somewhat limited in opportunities, and the font to 64 
characters per line not always easy to read. About him well

as well as other programs that I mention, we strongly recommend 
that you read complete description.



                  MASM


  Very similar to the "TASM", as the external
design and capabilities. Has
of "STS" and the import of TASM 3.
The good news is that the choice of a file for work carried out 
is not putting his name and the cursor. 

  Both of the above assembly language (and not
only they) have in their composition, such
standard features, like search in the text
fragment with the possibility of replacement, the inclusion
in assembling the text and the assembler code blocks from the 
disk, and, of course, input program text with its subsequent 
assembling. 


                  ALASM


  But this is a thing more powerful. This assembly provides the 
ability to customize the way the switch memory pages of your 
machine with loadable drivers written, again, in the format 
"ALASM". This gives the opportunity to work with several 
different texts simultaneously. It is also possible to change 
character set (font). Built-in "STS", obviously, has become the 
standard. 

  But it was not without flaws. To those may be the 
impossibility of the compilation of texts of several pages at 
once, the complexity of the syntax and indication errors. And 
most importantly - received after compiled code can not be 
burned to CD means of the assembler. For this

have to use Basic or "STS".


                  ZX-ASM


  It implemented a different approach. If
in previous assemblers is controlled by keyboard shortcuts, then
"ZX-ASM" has an extensive menu system. But
At the same time, it is certain
inconvenience, since the choice of the necessary
function goes sometimes too much (in
Anyway, for me) time.


                   XAS


  In general, leaves a very pleasant experience. Scrolling text 
is quite rapidly accelerated disc surgery. Can

work with texts in two pages. And Podgruzka text when assembling
going into the second page, thereby
it is possible to process at a time
up to 30 KB of text. There is also a transcoder
(File) to convert text
other formats in "XAS". Another page
reserved for macros that can, at any time to edit. There is a 
possibility of reduced recruitment and avtotabulyatsiya. 

  Fly in the ointment: the inability to change with
search in the text, there is no priority in arithmetic. There 
are no function "Merge", but it pays the possibility of 
transfer of text from page to page.



                  STORM


  Scrolling text here is ... well
very fast! This applies to the assembly. Abbreviated dialing 
and avtotabulyatsiya, the right priorities in arithmetic 
operations, as well as a very quick search text.


  The disadvantages are unusual
management and the inability to work simultaneously with 
multiple texts. 


                   STS


  Well, here we get to it. As already
mentioned, this is a monitor program. AND
I say again, that for the moment replace her
you will not find, for "STS", literally
words, is indispensable for the 128-x machines. With its
means you can monitor the status of
all computer resources in the process step by step
execution (trace) program in machine code. In this screen you 
watch full-length dizasseblera rather than binary numbers. 

  From version to version "STS" improved, acquiring new 
features. There version 3.2 with the ability to view unit

data as graphs. A version of "STS 4.3 + @"
provide an opportunity to conveniently work with
MAGIK-files.

  In short, take and use. Not
sorry!



             In conclusion ...


  Come to an end of an introductory course. Must
add that the advantages and disadvantages Asseblerov I have 
described is not everything, but it already - self-paced ...


  It remains to you to pick yourself right
tool and wait for the continuation of this
article in which we try to understand
already specifically with the assembly language.

  All the described software you
help find our editorial staff. At the same time add that 
without your letters and calls we do not can give the 
information that you really need!


  Coordinates, as amended, and my
own, you'll find on our site
"About".

  See you!