Source : Free On-Line Dictionary of Computing

RCA 1802
     
         An extremely simple {microprocessor} fabricated in
        {CMOS}, running at 6.4 MHz at 10V (very fast for 1974).  It
        could be suspended with the clock stopped.  It was an 8-bit
        processor, with 16-bit addressing.  Simplicity was the primary
        design goal, and in that sense it was one of the first {RISC}
        chips.  It had sixteen 16-bit {registers}, which could be
        accessed as thirty-two 8-bit registers, and an {accumulator} D
        used for arithmetic and memory access - memory to D, then D to
        registers and vice versa, using one 16-bit register as an
        address.  This led to one person describing the 1802 as having
        32 bytes of {RAM} and 65535 I/O ports.  A 4-bit control
        register P selected any one general register as the {program
        counter}, while control registers X and N selected registers
        for I/O Index and the operand for the current instruction.
        All instructions were 8 bits - a 4-bit {op code} (total of 16
        operations) and 4-bit {operand register} stored in N.  There
        was no real {conditional branching}, no {subroutine} support
        and no actual {stack} but these could be implemented by clever
        use of registers, e.g. changing P to another register allowed
        jump to a subroutine.  Similarly, on an interrupt P and X were
        saved, then R1 and R2 were selected for P and X until an {RTI}
        restored them.
     
        The {RCA 1805} was an enhanced version.
     
        The 1802 was used in the {COSMAC} (VIP?) {microcomputer} kit,
        some video games from {RCA} and {Radio Shack}, and the
        {ETI-660} computer.  It was chosen for the Voyager, Viking and
        Galileo space probes as it was also fabricated in {Silicon on
        Sapphire}, giving radiation and static resistance, ideal for
        space operation.
     
        {More history (http://www.cosmacelf.com)}.
     
        (2002-04-09)