Editing National Semiconductor SC/MP (section)

{{Short description|8-bit microprocessor}}
{{Infobox CPU
|name         = National Semiconductor SC/MP
|image        = National Semiconductor SCMP-die.jpg
|caption      = PMOS SC/MP die (ISP-8A/500)
|produced-start={{Start date and age|April 1976}}
|produced-end = 
|slowest      = 1 |slow-unit=MHz
|fastest      = 4 |fast-unit=MHz
|manuf1=[[National Semiconductor]]
|arch         = 
|transistors  = 
|numinstructions = 
|data-width   = [[8-bit computing|8 bits]]
|address-width=[[16-bit computing|16 bits]]
|pack1=40-pin [[Dual in-line package|DIP]]
|predecessor  = 
|successor    = 
}}
[[National Semiconductor]]'s '''SC/MP''' (pronounced ''scamp'') for '''Simple Cost-effective Micro Processor''', is an early [[8-bit computing|8-bit]] [[microprocessor]] which became available in April 1976. It was designed to allow systems to be implemented with the minimum number of additional support [[integrated circuit|chips]]. SC/MP included a daisy-chained control pin that allowed up to three SC/MP's share a single main memory to produce a [[multiprocessor]] system, or to act as controllers in a system with another main [[central processing unit]] (CPU). Three versions were released over its lifetime, SCMP-1 through 3, the latter two also known as '''INS8060''' and '''INS8070'''.

To lower cost, the system used a bit-serial [[arithmetic logic unit]] (ALU) and was thus significantly slower than contemporary designs like the [[Intel 8080]] or [[MOS 6502]] which had parallel ALUs. Another oddity was that the [[program counter]] could only access the lower 12-bits of the [[16-bit]] address, and the upper 4-bits had to be set using special instructions. The result was that instructions accessed [[main memory]] as sixteen 4&nbsp;kB "pages" and reaching memory outside those pages required multiple instructions.{{efn|This segmented memory approach was more famous in the [[Intel 8088]].}}

The combination of slow speed and paged memory limited its attractiveness outside the embedded markets it was aimed at, and in this market it competed against the [[Fairchild F8]] which had a number of useful additional features. The system saw relatively little use.