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 for RCA 1802
From The Free On-line Dictionary of Computing (30 December 2018) :

  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.
     http://cosmacelf.com)">More history (http://cosmacelf.com).

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