eprom

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eprom (dict)

An EPROM, or erasable programmable read-only memory, is a type of computer memory chip that retains its data when its power supply is switched off. In other words, it is non-volatile. It is programmed by an electronic device that supplies higher voltages than those normally used in electronic circuits. Once programmed, an EPROM can be erased only by exposing it to strong ultraviolet light. EPROMs are easily recognisable by the transparent window in the top of the package, through which the silicon chip can be seen, and which admits UV light during erasing. A programmed EPROM retains its data for about ten to twenty years and can be read an unlimited number of times. The erasing window must be kept covered to prevent accidental erasure by sunlight. Old PC BIOS chips were often EPROMs, and the erasing window was often covered with a label containing the BIOS publisher's name, the BIOS revision, and a copyright notice. Some microcontrollers, often those from before the era of Flash Memory, use EPROM to store their program. This is useful for development, as using one-time programmable devices would be horribly wasteful for debugging. The EPROM was invented by engineer Dov Frohman. EPROMs come in several sizes both in physical packaging as well and storage capacity

EPROM Type	Size - bits	Size - bytes	Length (hex)	Last address (hex)
2716, 27C16	16Kbits	2KBytes	800	007FF
2732, 27C32	32Kbits	4KBytes	1000	00FFF
2764, 27C64	64Kbits	8KBytes	2000	01FFF
27128, 27C128	128Kbits	16KBytes	4000	03FFF
27256, 27C256	256Kbits	32KBytes	8000	07FFF
27512, 27C512	512Kbits	64KBytes	10000	0FFFF
27C010, 27C100	1Mbit	128KBytes	20000	1FFFF
27C020	2Mbit	256KBytes	40000	3FFFF
27C040	4Mbit	512KBytes	80000	7FFFF

NOTE: 27x series EPROMs containing a C in the name are CMOS based, without the C are NMOS

Eprom

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