27128 EPROM PDF
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Computer memory that can retrieve stored data after a power supply has been turned off and back on is called non-volatile. It is an array of floating-gate transistors individually programmed by an electronic device that supplies higher voltages than those normally used in digital circuits. Once programmed, an EPROM can be erased by exposing it to strong ultraviolet light source such as from a mercury-vapor light.
EPROMs are easily recognizable by the transparent fused quartz window in the top of the package, through which the silicon chip is visible, and which permits exposure to ultraviolet light during erasing. Development of the EPROM memory cell started with investigation of faulty integrated circuits where the gate connections of transistors had broken. Stored charge on these isolated gates changed their properties.
Each field-effect transistor consists of a channel in the semiconductor body of the device. Source and drain contacts are made to regions at the end of the channel. An insulating layer of oxide is grown over the channel, then a conductive silicon or aluminum gate electrode is deposited, and a further thick layer of oxide is deposited over the gate electrode.
The floating-gate electrode has no connections to other parts of the integrated circuit and is completely insulated by the surrounding layers of oxide.
A control gate electrode is deposited and further oxide covers it. 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 8-bit byte of storage to the output buffer amplifiers.
Each bit of the word is a 1 or 0, depending on the storage transistor being switched on or off, conducting or non-conducting. The switching state of the field-effect transistor is controlled by the voltage on the control gate of the transistor. Presence of a voltage on this gate creates a conductive channel in the transistor, switching it on. In effect, the stored charge on eprrom floating gate allows the threshold voltage of the transistor to be programmed.
Storing data in the memory requires selecting a given address and perom a higher voltage to the transistors. This creates an avalanche discharge of electrons, which have enough energy to pass through the insulating oxide layer and accumulate on the gate electrode.
When the high voltage is removed, the electrons are trapped on the electrode. Epro programming process is not electrically reversible. To erase perom data stored in the array of transistors, ultraviolet light is directed onto the die.
Photons of the UV light cause ionization within the silicon oxide, which allow the stored charge on the floating gate to dissipate. Since the whole memory array is exposed, all the memory is erased at the same time. The process takes several minutes for UV lamps of convenient sizes; sunlight would erase a chip in weeks, and indoor fluorescent lighting over several years.
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. A programmed EPROM retains its data for a minimum of ten to twenty years,  with many still retaining data after 35 or more years, and can be read an unlimited number of times without affecting the lifetime.
The erasing window must be 27218 covered with an opaque label to prevent accidental erasure by the UV found in sunlight or camera flashes. Often this label was foil-backed to ensure its opacity to UV.
Exposure time for sunlight of one week or three years for room fluorescent lighting may cause erasure. The recommended erasure procedure is exposure to UV light at Erasure, however, has to be accomplished by non-electrical methods, since the gate electrode is not accessible electrically. 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.
This method of erasure allows complete testing and correction of a complex memory array before the package is finally sealed. 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. The effects of this process on the reliability of the part would have required extensive testing so they decided on the window instead. EPROMs had a limited but large number of erase cycles; the silicon dioxide around the gates would accumulate damage from each 271228, making the chip unreliable after several thousand cycles.
EPROM programming is slow compared to other forms of memory. Because higher-density parts have little exposed oxide between the layers of interconnects and gate, ultraviolet erasing becomes less practical for very large memories. Even dust inside the package can prevent some cells from being erased. For large volumes of parts thousands of pieces or moremask-programmed ROMs are the lowest cost devices to produce.
EPROM – Wikipedia
However, these require many weeks lead time to make, since the artwork for an IC mask layer must be altered to store data on the ROMs. Initially, it was thought that the EPROM would be too expensive for mass production use and that it would be confined to development only. It was soon found that small-volume production was economical with EPROM parts, particularly when the advantage of rapid upgrades of firmware was considered.
Like EPROM chips, such microcontrollers came in windowed expensive versions that were used for debugging and program development. The same chip came in somewhat cheaper opaque OTP packages for production.
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. The first generation devices were fabricated with the p-MOS techology. While parts of the same size from different manufacturers are compatible in read mode, different eprok added different and sometimes multiple programming modes leading to subtle differences in the programming process.
This prompted larger capacity devices to introduce a “signature mode”, allowing the manufacturer and device to be identified by the EPROM sprom. However, as this was not universal, programmer software also would allow manual setting of the manufacturer and device fprom of the chip to ensure proper programming. From Wikipedia, the free encyclopedia. Digital Design and Fabrication. Cambridge University Press, p.
27128A – 27128A 128K EPROM Datasheet
Archived PDF from the original on International Trade Commission, ed. Retrieved from ” https: Non-volatile memory Integrated circuits Computer memory. All 271128 with unsourced statements Articles with unsourced statements from October Commons category link from Wikidata Wikipedia articles with GND identifiers.