Fairchild F8

Fairchild F8

F3850, the CPU of the Fairchild F8 system.
General information
Launched	1975
Common manufacturer	Fairchild Semiconductor
Performance
Max. CPU clock rate	1 MHz to 2 MHz
Architecture and classification
Instruction set	8-bit
Physical specifications
Package	40-pin DIP

The Fairchild F8 is an 8-bit microprocessor system from Fairchild Semiconductor, announced in 1974 and shipped in 1975.^[1][2] The original processor family included four main 40-pin integrated circuits (ICs); the 3850 CPU which was the arithmetic logic unit, the 3851 Program Storage Unit (PSU) which contained 1 KB of program ROM and handled 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 was another optional system that added 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 Intel 8080 or Motorola 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 greatly improved single-chip implementation, the Mostek 3870. It merged the 3850 and 3851 and reduced the number of power supply voltages. 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.