Donor challenge: Your generous donation will be matched 2-to-1 right now. Your $5 becomes $15! Dear Internet Archive Supporter,. I ask only. The Intel is a 5V only, ,bit Ultraviolet Erasable (Cerdip)/plastic production reside in a EPROM directly on a system’s memory bus. D K (32Kx8) uv EPROM in a 28 pin CERDIP package by Intel. Download Intel D datasheet: Status: NOS (New Old Stock), perfect condition.

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By using this site, you agree to the Terms of Use and Privacy Policy. Presence of a voltage on this gate creates a conductive channel in the transistor, switching it on. Since the whole memory array is exposed, all the memory is erased at epro, same time. To retrieve data from the EPROM, the address represented by the values at the address pins of the EPROM is decoded and used to connect one word usually an 2256 byte of storage to the output buffer amplifiers.

Views Read Edit Eeprom history. Even dust inside the package can prevent some cells from being erased. The effects of this process on the reliability of the part would have required extensive testing so they decided on the window instead.

Like EPROM chips, such microcontrollers came in windowed expensive versions that were used for debugging and program development.

IC Datasheet: EPROM : Free Download, Borrow, and Streaming : Internet Archive

Leaving the die of such a chip exposed to light can also change behavior in unexpected ways when moving from a windowed part used for development to a non-windowed part for production.

It was soon found that small-volume production was economical with EPROM parts, particularly when the advantage of rapid upgrades of firmware was considered. Archived PDF from the original on Source and drain contacts are made to regions at the end of the channel. The erasing window must be kept covered with an opaque label to prevent accidental erasure by the UV found in sunlight or camera flashes.


Each bit of the word is a 1 or 0, depending on the storage transistor being switched on or off, conducting or non-conducting.

Each field-effect transistor consists of a channel in the semiconductor body of the device. A programmed EPROM retains its data for a minimum of ten to twenty years, [5] with many still retaining data after 35 or more years, and can be read an unlimited number of times without affecting the lifetime.

Initially, it was thought that the EPROM would be too expensive for mass production use and that it would be confined to development only.

In other projects Wikimedia Commons. Exposure time for sunlight of one week or three years for room fluorescent lighting may cause erasure. In other words, to erase your EPROM, you would first have to X-ray it and then put it in an oven at about degrees Celsius to anneal semiconductor alterations caused by the X-rays. An insulating layer of oxide is grown over the channel, then a conductive silicon or aluminum gate electrode is 272566, and a further thick layer of oxide is deposited over the gate electrode.

The same chip came in somewhat cheaper opaque OTP packages for production. As the quartz window is expensive to make, OTP one-time programmable chips were introduced; here, the die is mounted in an opaque package so it cannot be erased after programming — this also eliminates the need to test the erase function, further reducing cost.

Development of the EPROM memory cell started with investigation of faulty integrated circuits where the gate connections of transistors had broken.

EPROMs had a limited but large number of erase cycles; the silicon dioxide around the gates would accumulate damage from each cycle, making the chip unreliable after several thousand cycles.


The first generation devices were fabricated with the p-MOS techology. Often this label was foil-backed to ensure its opacity to UV. To 27526 the data stored in the array of transistors, ultraviolet light is directed onto the die.

27256 – 27256 256K EPROM Datasheet

This creates an avalanche discharge of electrons, which have enough erom to pass through the insulating oxide layer and accumulate on the gate electrode. For large volumes of parts thousands of pieces or moremask-programmed ROMs are the lowest cost devices to produce.

Magnetic tape Hard disk drive.

This method of erasure allows complete testing and correction of a complex memory array before the package is finally sealed. Once programmed, an EPROM can be erased by exposing it to strong ultraviolet light source such as from a mercury-vapor light. 272566 the high voltage is removed, the electrons are trapped on the electrode.

27256 EPROM

Photons of the UV light cause ionization within the silicon oxide, which allow the stored charge on the floating gate to dissipate.

Storing data in the memory requires selecting a given address and applying a higher voltage to the transistors. Digital Design and Fabrication. Shining ultraviolet light on any part of an unpackaged device causes a photocurrent to flow from the floating gate back to the silicon substrate, thereby discharging the gate to its initial, uncharged condition photoelectric effect.

Erasure, however, has to be accomplished by non-electrical methods, since the gate electrode is not accessible electrically. Computer memory that can retrieve stored data after a power supply has been turned off and back on is called non-volatile.

International Trade Commission, ed.