Microsoft BASIC Decoded and Other Mysteries

written by Matthew Reed

There were many books that documented and disassembled the TRS-80 Model I ROM, but Microsoft BASIC Decoded and Other Mysteries by James Lee Farvour was the most famous.¹ Microsoft BASIC Decoded and Other Mysteries, volume 2 in the IJG’s TRS-80 Information Series, includes a complete overview of the Level II ROM in the TRS-80 Model I and is one of the best sources of information about the TRS-80 BASIC ROM. It cost $29.95 when it was introduced in 1981. A January 1982 review in 80 Micro said “Without a doubt, it is the most comprehensive book on Level II BASIC ROM to be published so far.”

Microsoft BASIC Decoded and Other Mysteries is made up of two sections. The first half of the book collects details about BASIC, including items not commonly found elsewhere. This includes reserved BASIC keywords, functions and entry points, the format used for cassette storage, even the formulas used by the BASIC math functions such as SIN and COS. One chapter covers disk operating systems, which weren’t even part of Microsoft BASIC.

The final chapter of the book takes up the entire second section. It is a complete disassembly of the original Level II ROM for the Model I. The listing, formatted like the NEWDOS disassembler output, comprises most of the book. The main attraction of the listing is the extensive comments, which are so detailed they often extend into the opposite page margin.

The disassembled listing is complete, with one exception: it lacks what are described as “extended mnemonics.”² For example, JR NZ,006DH is truncated to just JR. The hexadecimal opcodes are included, making it easy to reconstruct the missing detail if needed.

The complete mnemonics were presumably omitted to comply with copyright law and avoid the ire of Microsoft. According to Dennis Báthory-Kitsz, IJG never asked Microsoft for a license before publishing this book.³ Even with the less settled copyright law at the time, it is remarkable IJG dared publish something with “Microsoft” in the title.

One unusual thing about the book is the binding. It says:

Unlike most books, this book is made to come apart. Due to the unique nature of the subject matter and the use to which it will be put, its pages may be removed and inserted into a three ring binder. The pages are pre-drilled, and the binding is such that the pages may be removed with little effort.

Unfortunately, this means the pages tend to fall out over time. Despite mentions of three-ring binders, I’ve never seen a copy that had pre-punched pages.

In 1982, James Lee Farvour followed up with TRSDOS 2.3 Decoded and Other Mysteries, another full disassembly—this time with permission from Radio Shack. In 1984, IJG published Dale Buscaino’s IBM Basic Decoded and Other Mysteries; it’s unclear if IBM or Microsoft permission was sought.