Fairchild F8 definition processor
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 registers
, accessed by the ISAR register in cells (register windows) 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 CPUs, 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.