Based on his participation in the basic circuit design, definition, and system design of the Motorola 6800 microprocessor and supporting computer chips, Mensch is a co-holder of several 6800 family patents, including the 6800 central processing unit, 6820/21 Peripheral Interface Adapter, 6850 Asynchronous Communications Interface Adapter, and 6860 modem chip. He was the sole IC design engineer of the 6820/21 PIA, which was the first peripheral IC to have bit-programmable input/output. Along with three other engineers at MOS Technology, Mensch holds the patent on the decimal correct circuitry in the 6502 CPU. He was responsible for the design of basic circuits, oscillator, and buffer, transistor sizing, and instruction decode logic; wishing to minimize the number of levels of logic to achieve faster operation. Before leaving MOS Technology in 1977, Mensch became their microprocessor design manager.
Shortly after founding the Western Design Center in 1978, Commodore International contracted WDC to develop what they called a "macro-micro", a macro-programmed complementary metal–oxide–semiconductor processor that could be used in a small and powerful calculator. However, WDC was unable to complete the project, and Commodore ended their relationship with the new company. The first major effort of Mensch and his team was developing the WDC 65C02, an enhanced version of the NMOS 6502 microprocessor. The 65C02, in addition to being implemented in CMOS circuit technology that reduced power use and improved noise immunity, added some new instructions, and corrected several defects in the NMOS 6502. The 65C02 was subsequently adopted for use in the Apple IIc computer and, later, in an enhanced version of the Apple IIe. Mensch's next design, which was to become an important product at WDC, was a 65C02-compatible 16-bit microprocessor, the 65C816, later designated W65C816S. The 65C816's design came about following consultation with Apple and was adopted by them for use in the Apple IIGS computer. The 65C816 was later chosen as the core of the Ricoh 5A22 processor that powered the popular Super Nintendo Entertainment System. Mensch developed the Mensch Computer as a means to promote the W65C816S microprocessor. It was a system designed around the WDC W65C265S microcontroller, which contains a W65C816S core. The computer, which includes the Mensch Works software suite, was produced for a time by WDC and was made for hobby and education uses. , Mensch was still involved with design engineering at WDC, along with his work as CEO. He has written the upcoming Terbium processor family's datasheets and will be making the major register-transfer level design decisions associated with that processor microarchitecture. Chuck Peddle and Bill Mensch are regarded as personal computer pioneers, because both the 6502 technology and business model were instrumental in helping launch the personal computer revolution.
