Programmable ROM: Difference between revisions

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{{Memory types}}

{{short description|TypeWrite of solid stateonce computer memory that becomes read only after being written once}}

A '''programmable read-only memory''' ('''PROM''') is a form of digital memory where the contents can be changed once after manufacture of the device. The data is then permanent and cannot be changed. It is one type of [[read-only memory]] (ROM). PROMs are usually used in digital electronic devices to store permanent data, usually low level programs such as [[firmware]] or [[microcode]]. ThePROMs keymay differencebe fromused aduring standarddevelopment [[Read-onlyof memory|ROM]]a issystem that thewill dataultimately isbe writtenconverted intoto aROMs ROM during manufacture, while within a PROMmass theproduced data is programmed into them after manufactureversion. Thus,These ROMstypes tendof tomemories beare used onlyin for[[microcontroller]]s, large[[video productiongame runsconsole]]s, withmobile wellphones, radio-verifiedfrequency data.identification PROMs([[RFID]]) maytags, beimplantable usedmedical wheredevices, thehigh-definition volumemultimedia requiredinterfaces does not make a factory-programmed ROM economical([[HDMI]]), orand duringin developmentmany ofother aconsumer systemand thatautomotive may ultimately be converted to ROMs in a mass produced versionproducts.

PROMs are manufactured blank and, depending on the technology, can be programmed at the wafer, final test, or in system stage. Blank PROM chips are programmed by plugging them into a device called a ''PROM programmer''. CompaniesA cantypical keepPROM adevice supplyhas ofan blankarray PROMsof inmemory stock, and program them at the last minute to avoid large volume commitmentcells. These types of memories are frequently used inThe [[microcontroller]]s,bipolar [[video game consoletransistor]]s, mobile phones, radio-frequency identification ([[RFID]]) tags, implantable medical devices, high-definition multimedia interfaces ([[HDMI]]) and in manythe othercells consumer and automotive electronics products. A typical PROM device is made up ofhave an arrayemitter of memory cells, each made up of a transistor, whichthat is a [[bipolar transistor]], connected to a [[Fuse (electrical)|fuse]] called a [[polyfuse (PROM)|polyfuse]]. inTo theprogram emitter of the transistor. Aa PROM programmer is used to strategically blow the polyfuse, programming the PROMpolyfuses.<ref>{{cite book | url=https://books.google.com/books?id=9VHMBQAAQBAJ&dq=prom+fuse&pg=PA760 | title=The Electronics Handbook | isbn=978-1-4200-3666-4 | last1=Whitaker | first1=Jerry C. | date=3 October 2018 | publisher=CRC Press }}</ref>

== History ==

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=== One time programmable memory ===

OTP (one time programmable) memory is a special type of [[non-volatile memory]] (NVM) that permits data to be written to memory only once. Once the memory has been programmed, it retains its value upon loss of power (i.e., is non-volatile). OTP memory is used in applications where reliable and repeatable reading of data is required. Examples include boot code, encryption keys and configuration parameters for analog, sensor or display circuitry. OTP NVM is characterized, over other types of NVM like [[eFuse]] or EEPROM, by offering a low power, small area footprint memory structure. As such, OTP memory finds application in products from microprocessors & display drivers to power management ICs (PMICs).

Commercially available semiconductor antifuse-based OTP memory arrays have been around at least since 1969, with initial antifuse bit cells dependent on blowing a capacitor between crossing conductive lines. [[Texas Instruments]] developed a MOS [[gate oxide]] breakdown antifuse in 1979.<ref>See [http://patimg2.uspto.gov/.piw?Docid=4184207&idkey=NONE US Patent 4184207] {{Webarchive|url=https://web.archive.org/web/20180427183945/http://patimg2.uspto.gov/.piw?Docid=4184207&idkey=NONE |date=2018-04-27 }} - High density floating gate electrically programmable ROM, and [http://patimg2.uspto.gov/.piw?Docid=4151021&idkey=NONE US Patent 4151021] {{webarchive|url=https://web.archive.org/web/20180427092847/http://patimg2.uspto.gov/.piw?Docid=4151021&idkey=NONE |date=2018-04-27 }} - Method of making a high density floating gate electrically programmable ROM</ref> A dual-gate-oxide two-transistor (2T) MOS antifuse was introduced in 1982.<ref>[http://www.chipestimate.com/techtalk/techtalk_071218.html Chip Planning Portal]. ChipEstimate.com. Retrieved on 2013-08-10.</ref> Early oxide breakdown technologies exhibited a variety of scaling, programming, size and manufacturing problems that prevented volume production of memory devices based on these technologies.