История[ править править код ] Разработка ячеек памяти EPROM началась с расследования дефектности интегральных схем, в которых затворы транзисторов оказались разрушенными. Хранимые заряды в этих изолированных затворах изменили их свойства. Принцип действия[ править править код ] Разрез транзистора с плавающим затвором. Каждый полевой транзистор состоит из канала в полупроводниковой подложке устройства.
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The small quartz window admits UV light for erasure. 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 changes their threshold voltage. In , he noted the movement of charge through oxide onto a gate. Patent 3,, in 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. Each bit of the word is a 1 or 0, depending on the storage transistor being switched on or off, conducting or non-conducting.
A cross-section of a floating-gate transistor 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 the floating gate allows the threshold voltage of the transistor to be programmed. Storing data in the memory requires selecting a given address and applying 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.
The programming process is not electrically reversible. To erase the 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. Details[ edit ] Atmel AT27C - an OTP EPROM 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 kept 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 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. The effects of this process on the reliability of the part would have required extensive testing so they decided on the window instead.
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. 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.
While parts of the same size from different manufacturers are compatible in read mode, different manufacturers 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 programmer. However, as this was not universal, programmer software also would allow manual setting of the manufacturer and device type of the chip to ensure proper programming.
The 24U universal 24 pin EPROM replacement kit
This kit is a very small adapter board that can take a cheap and easy to find 28 pin EPROM , , , and can use it to replace a , or Note: the 24U will NOT replace a TMS Why I created this kit as I work on a lot of early 80s arcade games, and was getting tired of finding and stocking s and s. They are fairly hard to find without spending a lot of time, they are VERY expensive, and often the ones I received seemed bad as many would not program. I was pushed over the edge when I started working on bunch of boards that used s which many modern programmers will not program. This adapter board allow me to only buy one type of cheap and easy to find 28 pin EPROM chip and not have to stock so many other types. There is NO need to "double, triple, or quadruple" the image on the new chip, simply burn the original ,, or data file onto the new chip as-is. Note: if you have a v3 board you will have 2 extra jumpers these should be set be default as shown in this image. Ensure that these jumpers are as shown in the image.
2708 / 2704 EPROM reader / programmer
Хранимые заряды в этих изолированных затворах изменили их свойства. Принцип действия Разрез транзистора с плавающим затвором. Каждый полевой транзистор состоит из канала в полупроводниковой подложке устройства. Контакты истока и стока подходят к зонам в конце канала. Изолирующий слой оксида выращивается поверх канала, затем наносится проводящий управляющий электрод кремний или алюминий , и затем ещё толстый слой оксида осаждается на управляющем электроде.