Source : Free On-Line Dictionary of Computing

SC/MP
     
        (Nicknamed "Scamp") A typical 8-bit {microprocessor} from
        {National Semiconductor} released in April 1976.  It was
        intended for control applications (a simple {BASIC} in a 2.5K
        {ROM} was added to one version).  It featured 16 bit
        addressing, with 12 address lines and 4 lines borrowed from
        the data bus (it was common to borrow lines from the data bus
        for addressing).  Internally, it included three {index
        register}s (P1 to P3) and two 8-bit general-purpose
        {register}s.  It had a {PC}, but no {stack pointer} or
        {subroutine} instructions (though they could be emulated with
        index registers).  During {interrupt}s, the {PC} was saved in
        P3.  It was meant for embedded control, and these features
        were omitted for cost reasons.  It was also {bit serial}
        internally to keep it cheap.
     
        The unique feature was the ability to completely share a
        system bus with other processors.  Most processors of the time
        assumed they were the only ones accessing memory or I/O
        devices.  Multiple SC/MPs could be hooked up to the bus, as
        well as other intelligent devices, such as {DMA controller}s.
        A control line (ENOUT (Enable Out) to ENIN) could be chained
        along the processors to allow cooperative processing.  This
        was very advanced for the time, compared to other {CPU}s.
     
        In addition to I/O ports like the {Intel 8080}, the SC/MP also
        had instructions and one pin for serial input and one for
        output.
     
        (1994-11-16)