In this series we'll learn a simple self contained 'Hello World'... Well learn how to compile it, and run on an emulator, We'll then learn a more complex example, which includes a 'monitor' function which will show the status of the registers to screen.

Lesson H1 - Hello World on MS Dos In this lesson we'll learn to use DOS INTerrupt calls to show characters to the screen and return to DOS, we'll use this to show Hello World.

First we're going to define our program type to the assembler for a basic program .model small will work well. Next we need to define a stack - we'll define 1024 bytes with .stack 1024 We'll define a data segment (DS) with .data... we'll put our 'Hello World' Message in there Next we need our .code segment... We'll start our program by initializing the DS and ES registers to the data segment and code segment

When we want to print a character to the screen, we'll use INT 21h (dos int) function 02h (Output Character to Monitor) This prints the character in DL We'll write a function called PrintChar that prints the character in AL (this is to maintain compatibility with other platforms and tutorials)
We'll use this PrintChar routine to print a Char 255 terminated string We'll create a function called 'PrintString' which will print the string at address [ds:si]
When we want to start a new line, we can do this by printing Character 13, then Character 10
When we want to show the string, we need to make sure ds:si points to the 255 terminated string, To return to DOS we use INT 21h (Dos Int) function 4Ch - we can provide a return code to DO in AL

these tutorials use UASM as an assembler, it's free and MASM compatible! We compile it on the command line with the following command: Defined Symbols... We're defining some symbols on the command line (equivalent of the equ command).. you don't need this for the basic hello world MZ = EXE... MZ tells the assembler we're buiding an EXE file (rather than a COM file) Listing File... we're specify a listing file - it shows the source and resulting bytecode, it's for debugging, so you don't need it, but it helps! Output file... this is the resulting program file Source file... the ASM file we're compiling, in this example %buildFile% will be defined by the batchfile - it would be Hello.asm or something if you're writing your own build script
The file will be built into a DOS EXE file... Note, this probably won't work on modern windows,  so we'll run it with DOS BOX
We need to set up the Dosbox config file (dosbox.conf) to autoload our program
Here is the result

COM Files are limited to 64k in entirety - the .data and .code segments must all fit in 64k EXE files are more flexible Due to the removal of backwards compatibility, neither will probably work on modern machines - at least if they are 64 bit.

The monitor tools need some words of data to back up essential registers, these should be defined in the DATA segment
The Monitor tools need a PrintSpace function
We need to include the monitor tools as a separate file.

Writing your own monitor tools may seem a bit odd, but writing our own means we don't have to worry about the functionality our emulator does or does not provide. The Monitor tools are pretty complex, so we're not going to discuss their workings here!

Lesson H2 - Hello World on the WonderSwan / Wonderswan Color Let's take our 8086 on the road with some portable programming!... In this episode we'll take a look at the 186 based WonderSwan!

Beginning a Wonderswan program

In these tutorials we use some software debugging tools, A Monitor which shows the state of the registers, a Debugger which shows some lines of the memory
Here is the result

Lesson H3 - Hello World on MS Dos via Native Tools (MASM 6.11) We learned how to make Hello World from windows last time... This time we'll go FULL DOS (never go full dos!) and write and compile our program only using MSDOS software... no windows needed!

MASM_HLO.ASM

We'll need a copy of MASM611 somewhere... the one we're using here was downloaded from this site.

In this example we'll use the copy of MASM found here, First we should extract all the folders from our MASM archive into a folder on our Dos C Drive.
To start the installation we need to go in to the DISK1 folder of the files we just extracted Next we run SETUP.EXE
Install the software 'using defaults' (Option 2)
We'll use the MASM 'Programmers WorkBench' to write our program, but we need to set up the environment variables So lets create a batch file called "PWB.BAT" in C:\MASM611 - either with EDIT in dos if we have it, or NOTEPAD in windows. First we call the batch file 'NEW-VARS.bat' created by the installer. then we run PWB.exe in the BINR folder We can now run PWB to start the programmers editor	call binr\NEW-VARS.bat binr\PWB.exe

We can assemble our program with the EXECUTE command from the RUN command
Rebuild All will assemble our program
Oh Noes! we have errors!... Click View Results to see what went wrong!
We have done a naughty! Lets fix the bugs in our code!
We need to change [ds:si] to ds:[si] on line 24 of the old hello world example We also need to add END to the end of our program
If we build again we will get 2 warnings... but we don't care because we like to live dangerously and have no fear! Select Run Program
Our program now works fine! Hurrah!

It should be noted that using DOS is likely to make things harder for us programming than our advanced windows 7 machines (or even sucky windows 10 ones! :-P) So this isn't really the 'easiest' way to write dos programs!

Lesson H4 - Hello World on the PC9821 Although it may appear to be an IBM PC, The japanese PC9821 is not the same! The screen doesn't use CGA, EGA or VGA, and there is a second screen layer, exclusively for text characters! In this lesson we'll learn how to use the Text layer screen on the Japanese PC 9821.

P98_HelloWorld.asm P98_HelloWorld_Advanced.asm

The PC 9821 hardware is totally different to the IBM PC, and the bios calls all work differently too... however, there was a version of MS-DOS released, and the INT calls to DOS work the same. This means we can actually assemble the standard DOS Hello World and it will run on the PC9821, but in this example we'll do something different, draw characters direct to the memory of the Text layer!

Memory map

The Text layer's VRAM is at memory address $A0000 and $A2000

$A0000 contains the 16 bit character numbers (16 bit to support japanese)

$A2000 contains the 8 bit character attributes, Note that there is one unused byte after each attribute, so they are aligned with the 16 bit characters

20 bit address	Purpose
$A 0000	Text Characters (2 bytes per char)
$A 2000	Text Attributes %GRBVUrbs    (V=vertline U=Underline r=reverse b=blink s=secret (1=show / 0 = hide))
$A 4000	CG Window 4k
$A 5000
$A 8000	GVRAM0 Plane 0 B
$A BE80	GVRAM0 Plane 1 B
$A FD00
$B 0000	GVRAM1 Plane 0 R
$B 3E80	GVRAM1 Plane 1 R
$B 8000	GVRAM2 Plane 0 G
$B BE80	GVRAM2 Plane 1 G
$B FD00
$C 0000	EMS Memory Window 32k x 4
$D 0000	Kanji Ram
$D 4000	Dictionary Rom
$D 8000	KGC Rom
$D C000
$E 0000	GVRAM3 Plane 0 I
$E 3E80	GVRAM3 Plane 1 I

Beginning a PC98 DOS program

In these tutorials we use some software debugging tools, A Monitor which shows the state of the registers, a Debugger which shows some lines of the memory
Here is the result