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SJ Defender (talk | contribs) m Disambiguated: PROM → Programmable read-only memory |
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=== Program memory ===
For production use as [[embedded system]]s, the on-board [[Read-only memory|ROM]] would be either [[Programmable read-only memory|mask programmed]] at the chip factory or one-time programmed (OTP) by the developer as a [[Programmable read-only memory|PROM]]. PROMs often used the same UV EPROM technology for the chip, but in a cheaper package without the transparent erasure window. During program development it was still necessary to burn EPROMs, this time the entire controller IC, and so [[Zero insertion force|ZIF]] sockets would be provided.
With the development of affordable [[EEPROM]] and eventually [[flash memory]], it became practical to attach the controller permanently to the board and to download program code to it through a serial connection to a host computer. This was termed "[[in-circuit programming]]". Erasure of old programs was carried out by either over-writing them with a new download, or bulk erasing them electrically (for [[EEPROM]]) which was slower, but could be carried out in-situ.
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