Programming - a course of study assembler Wlodek Black.
5. - The course of study assembler -
(C) WLODEK BLACK
Hello, dear users!
In the beginning I allow myself to express my sincere gratitude
to the newspaper "NICRON" for the offer of cooperation. We are
talking about some correspondence courses on programming
language "Assembler". Actually, I've suggested this as one of
the options for my participation in such a steep undertaking.
It's no secret that among us, dear colleagues, many well-known
coders (which means programmers in assembly language). But how
many more do not display talent!
No loss (and vice versa, praising ...) the role of
"Inforkom"-a in the great cause assemblerizatsii (read their
books!), suggesting you something that can be called a synopsis
of lectures on the assembler. Y This synopsis is a couple of
advantages over the books "Inforkom" as: it can be sent over
the network and for him not to pay. But there is and
disadvantage: it is focused on the computer "MSX", which,
although and built on the same processor but differ as the
plane of locomotive. I just did not have time to make
adjustments! But I made them (So I'll make that ... !...),
especially as the Polytechnic I now could read assembler
course, not only for the MSX, but for the Spectrum.
000h.Vvedenie.ChTO CAN GIVE Mastering the assembler?
Hello, dear user! At this stage it is assumed that you
already are familiar with any high-level programming language,
BASIC, for example. At the same time you probably seen a lot of
computer games with great graphics and understand that this is
not napishesh.Na BASIC BASIC, like any other high-level
language, you can create only that the language allows. When
programming in assembler and the codes will be available for
all that enables the machine. Computer games provide an
opportunity to "feel the difference" even unprofessional.
Writing a program in a language the processor can help, even
when high-level language provides the necessary tools, but the
program is running slowly or too large. Programmer, who owns
native language processor, much easier to cope with the
problems of failures, software incompatibilities, need to adapt
programs to their conditions, etc. Some importance and have
questions "hacking" programs, "obessmerchivaniya" games against
malicious (viruses). Finally, knowledge of the machine up and
down gives with nothing comparable self-confidence, a sense of
their usefulness society. All of the most powerful, most
needed, the most sensational, yes and the most expensive
software is written in assembly language, at least for an 8-bit
machines.
CPU Z80, in addition to MSX-"wells" and "Daewoo", used
even in this super-popular PC as the Spectrum, and on
It is based on working telephone numbers avtoopredeliteli, PBX,
industrial robots, even children's toys. Z80 - the only
8razryadny processor continues to grow at the present time:
already established high-speed and sverhekonomichnye
modification, and progress is not going to stop. Z80 - the only
8-bit processor, the annual production volume is increasing. In
Russia it is released under the name K1810VM80 and KR1858VM1 -
normal and high-performance variants, respectively.
001h. Hands with eight fingers, Art Nouveau on the PCB,
1 +1 = 10 AND OTHER FUNNY THINGS.
CPU Z80 - eight-bit. The basic unit of information
with which it works - bytes. Byte - 8 bits. Binary system is
very simple. Each subsequent digit number over the previous 2
times.
128 64 32 16 8 4 2 1
* * * * * * * *
bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0
For example: a binary 11001011 is equal to:
1 1 0 0 1 0 1 1
128 + 64 + 8 + 2 + 1
= 203.
The number of ones in the number 8 "Kolov" equal 255.Takim
, the range of byte ranges from 0 to 255. With the 255 you
could meet in the games, "trampled" crackers - for example, to
255 and can be reduced the number of lives, cartridges, etc.
Binary representation of numbers in most cases not very
convenient - it is cumbersome, and not too prominently, a chain
of ones and zeros melteshaschy merge into a pattern, in which a
person can easily get confused and make mistakes. Therefore,
people came up with a more suitable record of binary numbers -
hexadecimal form. When byte in hex it is conventionally divided
into two nibbles of 4 bits each (in foreign literature can be
found discordant called "Nibble", in Russian same language use
the term "notebook" or just say "nibble"), each of which is
denoted by one symbol - the numbers from 0 to 9, and then the
letter A, B, C, D, E or F.
A two-byte integer that represents a single unit, called the
word. Word contains 16 bits. In hexadecimal it is written by
four characters.
In MSX-BASIC you have already encountered the hexadecimal
notation of numbers - for example, 'hF37D. In assembler, this
entry appears slightly differently: the number must necessarily
begin with a digit, so a hex-number, starting with the letter,
attributed to the beginning of 0, and the letter "h"
(hexadecimal - hex) put at the end - 0F37DH.
There are derived units - kilobytes, megabytes, gigabytes.
Kilobyte - is 1024 bytes. Megabyte - 1024 kilobytes. And so on.
Factor in 1024 was chosen instead of 1000 for two reasons:
first, 1024 in binary notation - a round number (10000000000;
in hex - 0400h); secondly, 1024 is close to the way a human
tysyache.Hodit joke: a novice programmer a kilobyte 1000 bytes,
and the experienced - a kilometer 1024 meters.
It is easy to calculate the value of two-byte words: maximum
it is equal to 65535 (0FFFFH).
Now imagine that situation. From zero bytes, we subtracted
unit. How much do you get? Imagine a tape counter footage tape.
What happens if you make one revolution counter back? Get 999.
At the same time 999 - a 0 - 1. Became be, 999 =- 1. If the
counter has 8 bits and thus only one unit per revolution, then
one turn back from the position would give 00000000 11111111,
ie 11111111 =- 1. Here we learned how to appear in binary form
negative numbers: Senior, 7 th, the bit can be used as an
indication of the sign - If it is 1, then the number -
negative. If we continue twist our counter back, making 128
revolutions reach value of 10000000 (binary). This - the limit
for the negative numbers on the basis of one byte. In decimal
it is equal to -128. Towards positive values limit is
01111111 binary, or 127 decimal. For the word range - from
-32768 to 32767.
If our counter was 00000001, then adding to it a
(Committing a turnover in advance), we get 00000010. Here goes,
that 1 +1 = 10.
Thus, the finding in the memory byte 0FFH, we can assume
that it's either 255, or -1. So how do you distinguish one from
another? The answer may seem surprising: no. Truth emerge only
when the byte will be used processor when performing any
komandy.Dlya each team there its hard and fast rule, as
interpreted byte of data - either as 8razryadnoe unsigned
integer (0 ... 255), or as a 7-bit with sign (-128 ... 127).
The word sign is a senior, 15, and bit.
Bytes and words, we need at every step. Bytes - the main
unit for arithmetic and logical operations processor computer
memory also has a byte-oriented. Word - the main unit for
memory addressing. Z80 can be directly address 64K of memory.
This is 65,536 cells, each of which is stored a byte. 16-bit
address bus and 8-bit data - the cornerstones of the processor
architecture. Architecture same computer, MSX-2 Complex - his
memory is more than 64K, and since the processor at the same
time is able to address only 64K of RAM computer has to be
divided into pages, toggle a certain way.
[End of 1 st Text].
(C) Wlodek Black.
Tel. (095) 462-8902
Vladimir.
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Programming - a course of study assembler Wlodek Black.
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