6502 assembly language subroutines. (book reviews) Steve Gray.

6502 Assembly Language Subroutines

The authors and the publisher apparently assume that if you don't know which computers use the 6502 microprocessor, you wouldn't be interested in this book, which doesn't reveal until page 54 that the 6502 is used in the Apple.

The first three chapters are tutorial, on General Programming Methods (with a quick summary for experienced programmers), Implementing Additional Instructions and Addressing Modes (how to add them), and Common Programming Errors. The 40-puls subroutines are contained in eight chapters, on Code Conversion, Array Manipulation and Indexing, Arithmetic, Bit Manipulation and Shifts, String Manipulation, Array Operations, Input/Output, and Interrupts. Three appendixes provide a summary of the 6502 instruction set, a programming reference for the 6522 interface adapter, and the ASCII character set. A 24-page glossary completes the book.

The book is as thorough as just about every Osborne publication, and just about as complex. Each subroutine is documented completely, including the purpose of the routine, procedure followed, registers used, execution time, program size, data memory required, special cases, entry and exit conditions, and examples.

Leventhal, already known for his clear, detailed writing about assembly language in several phblications, adds another star to his crown with this excellent book, "aimed at the person who wants to use assembly language immediately, rather than just learn about it.' This is not easy to read; the authors pack a great deal in each page, and a previous knowledge of assembler would help very much. If you have an Apple and want to know more than just Basic, to the extent you're willing to dig hard, buy this book.

Review Grade: A-