ALTAIR.COM
In much of my development work for building CPM programs for my S-100 system I actually build, edit, assemble and sometimes even execute the program first on an IBM PC  using Windows XP or Windows 7.  One day I hope to have an S-100 video board of the resolution that current PC video boards have but for now nothing compares with the editing convenience of Microsoft's Visual Studio when working with .Z80 or .ASM files.

While you can edit the programs under windows (Visual Studio), you need a "CPM emulator" to assemble them and/or execute them.  There are a few good CPM emulators for the PC available.  I like to work with Peter Schorn's AltairZ80 Simulator. He has put an enormous amount of work into building a Windows based program that behaves as if your PC was a S-100 Altair computer.  Start with this documentation for some background information.  However to assemble and run your own CPM programs you only need to launch the CPM3 emulator within the core Altair.com program itself. From then on (transparent to you) you are operating under CPM3 in a Windows box.
Here is what you must do:-

You can download Peter's must current version of the simulator (SIMH) as a .zip file from here. That site has an enormous amount of information. Alternatively I selected just enough to get you a functional system to allow you to run CPM3 to assemble/run .z80 or .asm programs under the simulator quickly.  The process may seem a little complex/convoluted at first, but you will soon find yourself using it all the time.  A step by step process...

Bring up windows and open your "Windows Explorer" program.  Download the following .zip file Core SIMH Files.zip

Create a new folder, lets call it "Altair". Into that folder extract and place all the compressed files from the above Core SIMH Files.zip file.
You should have:-

altair80.exe 599K
app.dsk       1088K
cpm3           1K
cpm3.dsk     1088K
idsk             8192K

Double click on altair80.exe to launch the program.   This will create a SIMH specific DOS box window. At the "A>" prompt within that window type:-

do cpm3

After the carriage return you will see a completely self contained and functional CPM3 system. The box will look like this:-



The simulator behaves like a ~50MHz  Z80 driven system.  For example to see the user 0 directory type:-

DIR

You will see the normal CPM3 directory listing, something like this:-



You can read up on CPM3 to run many of these programs. Other "well known" programs have been added as well. They are marked as CPM3 "System files" so they can be run from any drive and user group. 

For our needs however we will take advantage of the fact that the simulator has an large (empty) memory disk "I:" drive that we will normally use as our work disk.

So typing "I:" CR will bring you to that drive.

Now we need some way of getting the windows based files into and out of this CPM simulator box.  The program R.COM and W.COM (both system files on A>) allow you to do this.  Suppose you have a file, say MASTER.Z80, which you have written in your windows "Altair" folder to get it into the CPM3 simulator I: drive at the I> prompt you type:-

r master.z80

and after the CR, the file is sucked on to the CPM3 I: drive.  There you can do anything you like with it under CPM3. Usually that involves assembling and linking it with CPM3 software.   When you are done, you write the resulting file (.HEX, .COM etc.) back to the Windows Altair folder at the I> prompt with:-

w master.hex

Now usually you will find yourself doing the same thing over and over again as you debug your program.  This is where we take advantages of CPM's submit file capability.  In the above example I have the following master.sub file on the CPM3 I: disk:-

r master.z80
z80asm master  FH
w master.hex
w master.lst

so if I type:-

submit master

I end up with a fully assembled master.hex file in the windows Altair folder ready for testing or EPROM burning.  The whole process becomes very automatic. You edit your .z80 or .asm code with Visual Studio (or your favorite editor) save the new version to disk, go to the above CPM3 box type, submit master and essentially instantly you have back the .hex file in your windows folder. Here is an example output:-



If there are assembly errors they will be listed.   Once you have your program is "hammered into shape" you can then upload it to your S-100 machine using a modem program such as described here.   The whole process works very smoothly mainly because the editing and assembly is so fast with modern PC machines.  Here is a typical working example screen picture:-
 


One further nice thing about this arrangement is if you close everything and save your whole Altair folder of contents, the next time you re-launch Altair.com it will start up where you left off. Nothing is lost.   Whatever windows folder Altair.com is launched from --  that is the folder the above "w.com" and "r.com" commands work with. You can even have multiple CPM3 boxes present and operating at the same time.

One subtle point, The CPM program HEXCOM (which converts a HEX file to a .bin) file behaves unexpectedly.  If you set a .Z80 program assembly org  at say 100H the program will generate a binary file correctly and you can use XModem to load it to RAM at 100H and run it.   If however you set the org to 1000H you have to subtract 100H bytes from the load location of the .bin file. So to run such a program at 1000H you would load it at F00H in RAM with XModem.

This page was last modified on 11/28/2020