English Computing Dictionary
Fairchild F8
An 8-bit {microprocessor}. The processor itself
had no {address bus} - program and data memory access were
contained in separate units, which reduced the number of pins
and the associated cost. It also featured 64 {register}s,
accessed by the ISAR register in cells ({register window}s) of
eight, which meant external {RAM} wasn't always needed for
small applications. In addition, the 2-chip processor didn't
need support chips, unlike others which needed seven or more.
The F8 inspired other similar {CPU}s, such as the {Intel
8048}. The use of the ISAR register allowed a subroutine to
be entered without saving a bunch of registers, speeding
execution - the ISAR would just be changed. Special purpose
registers were stored in the second cell (regs 9-15), and the
first eight registers were accessed directly. The windowing
concept was useful, but only the register pointed to by the
ISAR could be accessed - to access other registers the ISAR
was incremented or decremented through the window.