Fairchild F8

The Fairchild F8 is an 8-bit microprocessor system from Fairchild Semiconductor, announced in 1974 and shipped in 1975. The original processor family includes four main 40-pin integrated circuits (ICs); the 3850 CPU which contains the arithmetic logic unit and a scratchpad, the 3851 Program Storage Unit (PSU) which contains 1 KB of program ROM and handles instruction decoding, and the optional 3852 Dynamic Memory Interface (DMI) or 3853 Static Memory Interface (SMI) to control additional RAM or ROM holding the user programs or data. The 3854 DMA is another optional system that adds direct memory access into the RAM controlled by the 3852.

A minimal system containing a 3850 and 3851 also included four 8-bit data ports, 64 bytes of RAM, and a user program on ROM. This allowed microcontroller applications to be built using just two chips. Doing the same on more traditional designs like the 8080 or 6800 normally required seven. It also meant that any application that did not fit the simple requirements generally required at least three 40-pin ICs, the CPU, PSU and either the 3852 or 3853 along with additional memory chips. As a result of these tradeoffs, the F8 series found widespread use in the microcontroller market but saw less use as a CPU in general-purpose computers. It is relatively obscure today, as its embedded uses rarely revealed the F8 inside.

In 1977, Mostek released a significantly improved implementation, the Mostek 3870. It merged the 3850 and 3851 into a single chip and reduced the number of power supply voltages needed. More important, Mostek re-arranged the assembly line so user code in ROM was added at the last step, greatly reducing the cost of customizing the design for controller use. The 3870 replaced the original Fairchild versions and was produced by several companies in the US and Europe. In Europe, STMicroelectronics continued producing variations of the design into the mid-1990s.