Programming the 65816 Including the 6502, 65C02, and 65802 (1986)

Foreword

It was in July 1972, approximately one year after joining Motorola Semiconductor Products Division, Phoenix, Arizona, that I was first introduced to microprocessor design. Previously, I had worked on analog computers before graduating from Temple University in Philadelphia. While at the University of Arizona I worked on computer simulation of plasmas, simulating plasma reactions to radio frequency energy in search of a breakthrough enabling a nuclear fusion energy generation system (without radioactive waste) to become a reality. I graduated from the University of Arizona with a bachelor's degree in electrical engineering, majoring in digital semiconductor design with a minor in computer engineering.

Then in July 1972, I was faced with a major challenge. Rod Orgill and I were assigned the task that six engineers (two teams before us) had failed, which was to deliver a custom microprocessor to Olivetti of Italy. This was a very capable PMOS 8-bit microprocessor, which became a basis for the design approach of the Motorola 8-bit NMOS 6800. Rod (who now works for HP in Colorado) and I were successful; we were allowed to stay in design and become part of the 6800 design team. As you may be aware, the 6800 led to the 68000. As you may or may not be aware, it also led to the 6502.

In August of 1974, a few of us left Motorola and ended up at MOS Technology in Valley Forge, Pennsylvania. In September 1975 in the St. Francis Hotel in San Francisco, we introduced the NMOS 6502 with a purchase price of $25. Because of the price, Steve Wozniak and others could become familiar with this wonderful technology. At $375.00, (the price of the Intel 8080 and Motorola 6800), Steve and others would have bought a TV instead; with the 6502, we are talking about a computer chip selling for the price of an engineering textbook. And so the personal computer technology was born.

In May 1978, I founded the Western Design Center, Inc., in Mesa, Arizona. Our goal is to create the most affordable, highest performance, easiest to use, lowest power technology the world has seen. To this end we created the 65C02 in 1982 by using the low-power CMOS process (the same technology that lets a wristwatch run for a year off of a single battery). It is a direct replacement for the NMOS 6502. The 65C02 is destined to become the most used core microprocessor for a vast base of custom controller chips used in telephones, heart pacers, and more. The Apple //c was introduced in 1984 using the 65C02, and the Apple //e now uses it as well.

As Apple was introducing the Apple //c to the world, I was introducing to Apple the 16-bit version of the 65C02 known as the 65816. The 65816 will ultimately replace the 65C02 (as the 65C02 becomes used predominantly in one-chip microcomputers) and will become the midrange computer chip. Features have been selected that allow for complete emulation of the 6502 and 65C02 using the E (emulation) bit. (Incidentally, it was David Eyes who first suggested the E bit.) This saves a lot of software from premature obsolescence.

Other features were picked for high-level languages, cache memory, and recursive and reentrant code, just like the "big systems." There will be other generations. The 65832, for example, will have 32-bit floating point operations, in addition to 8- and 16-bit operations. It will plug into a 65816 socket and, of course, will be fully compatible with the 65C02 and 65816.

As the technology improves over the next 10 years and the density of integration increases, we expect to have full-size personal computers on one chip with only memory off chip. The memory cycle time for cache operation should approach 100 MHz, the speed of multimillion dollar mainframes. The power of the 65C02, in the same time frame, should drop to under 1 micro amp (the same as a watch chip) running off a watch crystal. Because the technology is low-power CMOS, low-cost packages are available, and heat generated is very low; therefore, low-cost environments can be built. The cost of the basic microprocessor chip will be under $5.00. And so, this same technology that will power human beings in heart pacers will also power telephones, communication networks, personal computers, and desk-top work stations. It is my belief that this technology will fuel world peace.

This book, as I see it, is and will become the vehicle that WDC will use to communicate not only to the layman, but also to the engineer. Within this edition many of the details of the operation exist. I hope the success of this edition will provide the basis for future editions which will include new details about the chip and system usage gained from industry experience, as well as information about new versions of the processors.

The development of these processors is not the work of one man: many have contributed directly and indirectly. I would like to thank a few of the people who have helped me through the years: Rod Orgill, E. Ray Hirt (vice-president of WDC), and Chuck Peddle who have given me many good ideas over the years; Lorenz Hittel who has suggested many features used on the 65C02 and 65816; Desmond Sheahan, Ph.D. and Fran Krch who, while at GTE Microcircuits, were instrumental in having the 65C02 and 65816 second sourced by GTE—a key to the early success of these programs; Apple computer engineers who suggested features for the 65816; Mike Westerfield who created the ORCA/M macro assembler; David Eyes and Ron Lichty who not only have written this book, which promises to be a classic, but also helped in the debug process by running some of the first software exploring various modes of operation; Will Troxell who has developed a high-performance board for the Apple // and a high-performance operating system exploiting the potential of the 65816; my sister, Kathryn, Secretary of WDC, and WDC's layout design manager who laid out the entire 65816; and the entire staff at WDC.

A special thanks to my wife, Dolores (Treasurer of WDC), who has given me much love, support, encouragement, laid out chips, taught layout designers, and given me four, happy, healthy, beautiful children.

William D. Mensch, Jr.
Mesa, Arizona
June 1985