{{Short description|Control line in digital electronics}} [[Image:SPI three slaves.svg|thumb|right|350px|An example SPI with a master and three slave select lines. Note that all four chips share the SCLK, MISO, and MOSI lines but each slave has its own slave select.]]
'''Chip select''' ('''CS''') or '''slave select''' ('''SS''') or '''chip enable (CE)''' is the name of a control line in digital electronics used to select one (or a set) of integrated circuits (commonly called "chips") out of several connected to the same computer bus, usually utilizing the three-state logic.<ref>{{cite web |last=Kalinsky |first=David |title=Introduction to Serial Peripheral Interface |date=February 2002 |url=http://www.embedded.com/electronics-blogs/beginner-s-corner/4023908/Introduction-to-Serial-Peripheral-Interface |accessdate=2 January 2013}}</ref><ref name="Ram2004">{{cite book|author=S. K. Venkata Ram|title=Advanced Microprocessor & Microcontrollers|url=https://books.google.com/books?id=MUI1ioZrnzcC&pg=PA94|year=2004|publisher=Firewall Media|isbn=978-81-7008-310-8|pages=94–}}</ref>
One bus that uses the chip/slave select is the Serial Peripheral Interface Bus (SPI bus).<ref name="Catsoulis2005">{{cite book|author=John Catsoulis|title=Designing Embedded Hardware|url=https://books.google.com/books?id=k9SbAgAAQBAJ&pg=PT176|date=16 May 2005|publisher=O'Reilly Media, Inc.|isbn=978-0-596-00755-3|pages=176–}}</ref>
When an engineer needs to connect several devices to the same set of input wires (e.g., a computer bus), but retain the ability to send and receive data or commands to each device independently of the others on the bus, they can use a chip select. The chip select is a command pin on many integrated circuits which connects the I/O pins on the device to the internal circuitry of that device.<ref name="Dandamudi2005">{{cite book|author=Sivarama P. Dandamudi|title=Guide to Assembly Language Programming in Linux|url=https://books.google.com/books?id=wS4EG0GyKXUC&pg=PA45|date=15 July 2005|publisher=Springer Science & Business Media|isbn=978-0-387-25897-3|pages=45–}}</ref>
When the chip select pin is held in the inactive state, the chip or device is "deaf", and pays no heed to changes in the state of its other input pins; it holds its outputs in the high impedance state, so other chips can drive those signals. When the chip select pin is held in the active state, the chip or device assumes that any input changes it "hears" are meant for it, and responds as if it is the only chip on the bus. Because the other chips have their chip select pins in the inactive state, their outputs are high impedance, allowing the single selected chip to drive its outputs.<ref name="Taylor2013">{{cite book|author=H.R. Taylor|title=Data Acquisition for Sensor Systems|url=https://books.google.com/books?id=eGTaBwAAQBAJ&pg=PA249|date=14 March 2013|publisher=Springer Science & Business Media|isbn=978-1-4757-4905-2|pages=249–}}</ref>
CS may also affect a power consumption or serve as cycle control in certain circuits (such as SRAM or DRAM).<ref>{{Cite web|url=https://www.jedec.org/standards-documents/dictionary/terms/chip-enable-input|title=chip-enable input {{!}} JEDEC|website=www.jedec.org|access-date=2019-05-21}}</ref>
==References== {{reflist}}
{{DEFAULTSORT:Chip Select}} Category:Computer buses {{electronics-stub}}