TABLE OF CONTENTS 1 FOREWORD……………………………………………………………………………………………………1 2 INTRODUCTION…………………………………………………………………………………………3 3 HOW TO USE THIS BOOK……………………………………………………………………4 4 DESCRIPTION OF DISK BASIC………………………………………………………5 FILE CONTROL BLOCK STRUCTURE………………………………………………6 FILE ALLOCATION TABLE…………………………………………………………………9 THE DIRECTORY………………………………………………………………………………………11 1793 FLOPPY DISK CONTROLLER DESCRIPTION…………………13 MACHINE LANGUAGE FILE INPUT/OUTPUT………………………………17 DISK BASIC RAM VARIABLES/BUFFERS……………………………………18 APPENDICES A MEMORY MAP B DISASSEMBLY OF DISK BASIC 1.1 C DISASSEMBLY OF DISK BASIC 1.0 D DISK BASIC SYMBOL TABLE – 1.1 E DISK BASIC SYMBOL TABLE – 1.0 F DISK BASIC ROUTINES AND ENTRY POINTS G DISK BASIC’S DATA/ASCII TABLES H DISK BASIC ERROR ENTRY POINTS I ASCII CHART DISK BASIC UNRAVELLED II FOREWORD ORIGINAL: SPECTRAL ASSOC REVISED:12/26/99 WALTER K ZYDHEK FOREWORD Due to the many requests for the Unravelled Series produced by Spectral Associates, and the fact that these books are rare and no longer in production, I have taken it upon myself to reproduce them in electronic .PDF (Adobe Acrobatâ) format. I have re-disassembled the ROMs listed in this book, and added all the comments from the Original Extended Basic Unravelled Book. Some changes were made to make the book a little easier to read. 1. The comments have been cleaned up some. In cases where a comments continued onto the next line, a * is placed in the Labels column, as well as a * at the beginning of each line of the comment. In cases where the previous comment used this format, a = was used. This was done in the original, but not all comments stuck to this format. 2. I have renumbered all the line numbers. Each Appendix (with code) starts at Line 0001. 3. Some spell checking, and context checking was done to verify accuracy. 4. I used the Letter Gothic MT Bold Font. This allows for display of Slashed Zeros. I thought it important to be able to distinguish between 0 and O. 5. All the Hex code now shows the Opcodes. There were other minor changes that were made to make viewing a little better. If any discrepancies arise, please let me know so that I may correct the errors. I can be contacted at: mailto:[email protected] Special Thanks to Jean-François Morin for pointing out those “Oops” to me. I’d like to also thank those who have either given me, or loaned me their copy of the original Unravelled Series. About Me My name is Walter K. Zydhek. I’ve been a Computer Hobbyist since 1984 when I received my 1st Tandy Color Computer 2 for Christmas. It had 32K of ram, Cassette, and one Cartridge. I quickly learned to program in Basic and then moved into Assembly. Over the next few years, I saved to purchase the Multi-Pak Interface, Disk Drives, Modem, OS-9, and various Odds and Ends. I moved to Tampa Florida and in the move, My CoCo was damaged. I then replaced it with the CoCo 3. WOW what a difference. I added the 512K Ram Upgrade, A CM-8 color monitor, and joined the Carolwood CoCo Club. (Thanks Jean-François for reminding me of the name.) I had a couple of close friends that helped me explore the world of CoCo and by this time, I knew that my CoCo would be my friend forever. I give special thanks to Steve Cohn, who helped me get started with ADOS. Two other people whose names I can’t remember were very beneficial to my mastering of the CoCo. Shortly after getting my CoCo 3, I started BBS’ing. Wow, a whole new world. My knowledge just kept growing. 1 DISK BASIC UNRAVELLED II FOREWORD ORIGINAL: SPECTRAL ASSOC REVISED:12/26/99 WALTER K ZYDHEK A few years later, I moved to Oregon, then to Phoenix, Arizona to attend school. I studied Electronics Technology at Phoenix Institute of Technology. In the second year, we studied Micro-processor Theory. For our labs, we just happen to use the Tandy Color Computer 3 (for studying 6809 Processors). I had it made. In this class I added an EPROM programmer/reader to my list of hardware. My favorite instructor, Gary Angle & I spent many hours sharing information on the CoCo. At one time, we shared a joint project to disassemble ROMs from industrial machinery, which used the 6809 Processor. Using the CoCo to read the ROMs to work with. I even had a BBS running under OS-9 at one time. RiBBS I think it was. Very similar to QuickBBS and RemoteAccess BBS for the PC. In 1991, I finally converted over to PC, but never forgetting my CoCo. About 5 years ago, My CoCo and all related material was stolen from me. And the CoCo world was just a memory. In the last 2 Years, my love for the CoCo has re-kindled. I have been partially content to use a CoCo Emulator for my PC. I tried the CoCo 2 Emulator by Jeff Vavasour. This was OK, but a lot was left out. I then purchased the CoCo 3 Emulator. Much better, but would not use “Double Sided Disks”. Although it did have a Virtual Hard Drive for use in OS-9. I then wanted to ‘better’ the CoCo Emulator, add use of PC hardware, Add Double Sided Disk functionality, and even make it Windows Native, instead of a Dos Box. Unfortunately I could not get the source code for the CoCo 3 Emulator. I then turned to Paul Burgin’s Dragon 2/Coco 2 Emulator. This had source code available and with a small $20.00 donation, was able to get the source code to additional portions of his program. I have tinkered with it, but came to understand that I needed more info on the CoCo. I have looked all over the net and found quite a lot of useful information, but what I really needed was the Unravelled Series. I was able to find someone that had Extended Basic Unravelled and Disk Basic Unravelled (He sent them to me for free). And a friend of mine had Super Extended Basic Unravelled (A copy I gave him years ago). Unfortunately, the books are not in the best of shape, and the type is hard to read, and with so many people looking for the books, I decided to re-do them in Electronic format. I ask everyone that obtains copies of this electronic document to PLEASE give freely. These books are for educational/informational use only. These books are no longer in publication and Spectral Associates no longer in business. Do not use these books for financial gain, as that would most certainly abuse the Copyright Laws that I have already bruised by re-producing them. Other than that, enjoy the books!! I’ll add more information to them as I get it. I plan on adding more Memory Map information, as well as hardware info in the coming months. But for now, take advantage of this fine resource. Walter K. Zydhek 2 DISK BASIC UNRAVELLED II INTRODUCTION ORIGINAL: SPECTRAL ASSOC REVISED:12/26/99 WALTER K ZYDHEK INTRODUCTION Disk Basic Unravelled will provide the reader with a complete detailed and fully commented assembly listing of the Disk Operating System (DOS) of Radio Shack’s COLOR BASIC. It is not within the scope of this book to teach the neophyte how to construct a DOS or to be able to completely understand the COLOR DOS. The reader will need to have a basic knowledge of 6809 assembly language programming to be able to take full advantage of the opportunities, which this book presents. It is also assumed that the reader is familiar with the contents of the Disk Basic Users manual, which contains a general description of the overall operation of Disk Basic and much useful information concerning the physical and logical format of the tracks & sectors. Disk Basic Unravelled will allow the reader to be able to completely understand the theory behind COLOR DOS to the point of being able to modify it for his own purposes or add extra commands or functions to the DOS. No attempt will be made to re—explain the functions of BASIC and Extended Basic, which were explained in the previous two books of the BASIC Unravelled series. The reader should be aware of the fact that Color Disk Basic is not a stand-alone system. There are many direct calls into the Basic and Extended Basic ROMs. These calls are not explained in this book; the reader will have to refer to the Basic and Extended Basic Unravelled books in order to get a full explanation of these ROM calls. A complete memory map of the system operating variables is given at the beginning of the DOS assembly listing and a symbol table showing the location of all referenced routines and tables is at the end of the listing. All of the ROMs used in the Color Computer have undergone revisions since the inception of the machine. The disk ROMs have undergone the most severe change of the three ROMs. The first disk RON (Revision 1.0) used only 6K of the available 8K RON space and the second disk RON (Revision 1.1) used approximately 6.5K of ROM with the majority of the .5K increase going to correct bugs in the first ROM and to add the DOS command to Disk Basic. That leaves 1.5K of free ROM space in the latest version of Disk Basic, which is available to the user if he has a 64K machine. It is not recommended that this free ROM space be permanently allocated by any user since the Disk Basic ROMs in the Dragon computer (a British clone of the Color Com- puter) use the entire 8K ROM space and have added several new disk BASIC commands.