EPROM

From Academic Kids

Missing image
VariousEPROMS.png
An assortment of EPROMS. The small windows admit UV light during erasure.

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.

Missing image
D8749.png
This 8749 Microcontroller stores its program in EPROM.

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
16 kbit
2KBytes
800
007FF
2732, 27C32
32 kbit
4KBytes
1000
00FFF
2764, 27C64
64 kbit
8KBytes
2000
01FFF
27128, 27C128
128 kbit
16KBytes
4000
03FFF
27256, 27C256
256 kbit
32KBytes
8000
07FFF
27512, 27C512
512 kbit
64KBytes
10000
0FFFF
27C010, 27C100
1Mbit
128KBytes
20000
1FFFF
27C020
2 Mbit
256 kbytes
40000
3FFFF
27C040
4 Mbit
512 kbyte
80000
7FFFF

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

See also

de:Eraseable Programmable Read Only Memory es:EPROM it:EPROM he:EPROM nl:EPROM ja:EPROM pl:EPROM sv:EPROM

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