{ If you have any comments or questions regarding this tutorial, please E-mail me } you have a copy of TASM, a necessary utility for writing assembly programs. [Those with programming experience in any other language may want to ignore. student use the Dos Debugger and the Microsoft Turbo Assembler (TASM). Editing It is used immediately after writing the Assembly language program. The tutorial is completely focused towards the computers that function with processors .. Example: C:\>tasm Turbo Assembler Version Borland.

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Well, I’ll start with the basics, gutorial instruction format and some simple instructions to manipulate registers. I don’t know how much you know about coding, so I’ll explain even the most simple stuff.

Please note, that I explain assembly coding. That means NO bit registers and instructions and NO protected- real- and virtual 86 mode for now. F irst of all, we’ll talk about the registers and then about the instructions to manipulate change them.

The has 14 bit registers, all with different usage see below. You might not understand some of the registers purposes, but be patient, I’ll explain everything later. You have the AH wssembly the AL register for example. All “flags” see below are stored here. All these flags have a name and purpose.

If you want to see all these register and flags, you can go to DOS and then start “debug” just type debug When you’re in debug, just type “r” and you’ll see all the registers and some abreviations for the flags. Type “q” to quit again. We won’t use debug to program in this tutorial, we’ll use a real assembler. I use TASM 3.

Assembly Programming Tutorial

If the processor stores a “word” bits it stores the bytes in reverse order in the memory. It looks like this: Okay, pretty clear huh?

Now let’s talk about segments. The divides it’s memory into segments. These numbers are stored in the segment registers see above. Three main segments are the code, data and stack segment. Segments overlap each other almost completely. If you start debug again and type “d” you can see some addresses at the left of the screen. The format is like this: The first number is the segment number and the second number is the offset within the segment.

As I said before, segments overlap. That means that segment begin at paragraph boundaries. Note that the offset 10h means the value 16 in decimal: Next, the other address Like I told you.


These are some basic things you need to know when you want to program in Assembly. Learn the registers and flags by heart and try to understand the segmentation of memory. On a or higher, you have something called real-mode and protected-mode. This Segment explanation is based on Real-mode, in Protected-mode it’s way different, but don’t bother, that’s real complicated stuff you don’t need to know.

But remember in the back of your head, that there’s more I know what I’m talking about. I’ll first give you the code and then I’ll explain it. I’ll explain the code now. Lines that start with a “. The lanfuage s behind it say what kind of info.

In this case it just tells the assembler the program is small and doesn’t need a lot of memory. I’ll get back on this later. Another line with info. This one tells the assembler that the “stack” segment starts here.

The stack is used to store temporary data.

Assembly Tutorial

It isn’t used in the program, but it must be there, because we make an. Code must be in procedures, just like in C or any other language. This indicates a procedure called main starts here. Procedures MUST have a start and end.

Borland’s Turbo Assembler – TASM | x86 Tutorial

It also tells the assembler were to start the program. Sssembly the procedure called txsm in this case. DB means Define Byte and so it does. In the data-segment it defines a couple of bytes. These bytes contain the information between the brackets. It’s called an “indentifier”. AX is a register. You use registers langyage the time, so that’s why you had to know about them before I could explain this. MOV is an instruction that moves data. It can have a few “operands” don’t worry, I’ll explain these names later Here the operands are AX and seg message.

Seg message can be seen as a number. It’s the number of the segment “message” is in The data-segment We have to know this languuage, so we can load the DS register with it. Else we can’t get to the bit-string in memory. The number is loaded in the AX register. MOV always moves data to the operand left of the comma and from the operand right of the comma.

The MOV instruction again. Here it moves the number in the AX register the number of the data segment into the DS register. We have to load this DS asse,bly this way with two instructions Just typing: This time it load the AH register with the constant value nine. This intructions stores the offset within the datasegment of the bit-string message into the DX register.


This offset is the second thing we need to know, when we want to know where “message” is in the thtorial. So now we have DS: See the segment explanation above. This instruction causes an Interrupt. The processor calls a routine somewhere in tassm. INT’s are very important and I’ll explain more of them later, since they’re also very, very complex. However, for now assume that it just calls a procedure from DOS.

The procedure looks at the AH register to find out out what it has to do. In this example the value 9 in the AH register indicates that the procedure should write a bit-string to the screen. Load the Ax register with the constant value 4c00h int 21h: The same INT again.

The value of AL is used as an “exit-code” 00h means “No error” That’s it!!! The debug screen atsm appear. When you are in the debugger, type “d”. You see some addresses and our program. Now type “u” you’ll see a list that looks like this: BF is the machine code of the mov ax,0f79 instruction. B8 means “mov ax,” and F is the number. The other instruction lea dx,message turned into mov dx,0. Let’s look at that address. Look at the right of the screen and you can see the message.

Now let’s tutoorial another address for the data. That would give you 0F77 the code segment. Two segments further means 32 bytes further, and that means an offset of So at this location the data is: Check by typing “d 0f Please note that it’s the SAME data. We can see it at multiple addresses only because the segments overlap! But in the program we said the data had to be in a langguage. Well, it IS in a data-segment, the data is just stored directly behind the code, but that doesn’t matter.