EPROM
An EPROM (English acronym for erasable programmable read-only memory, literally, erasable programmable read-only memory ) is a non-volatile electronic memory block that has been previously used primarily in computer technology, but now largely superseded by EEPROM.
This module type is with special programming equipment (called " EPROM burner " ) programmable. It can also be cleared by UV light and then reprogrammed. After about 100 to 200 deletes the EPROM has reached the end of its life. The deletion necessary for quartz glass window ( normal glass is not UV transparent ) makes the housing is relatively expensive. Therefore, there is no window types that are writable only once ( One Time Programmable, OTP).
Design and operation
An EPROM includes an array of memory cells in each of which a transistor representing a bit. A memory cell comprises a MOSFET transistor with an insulated auxiliary electrode, the floating gate. In programming, a higher voltage is applied so that charged by the avalanche effect, the floating gate. Thus, the driving voltage at which the transistor turns on shifts. The data can now be read as often, the sense voltage is below the programming voltage. The ultraviolet radiation used to erase the effect of the ionization of a large-area semiconductor material so that the previously deposited electrical charge can leave the floating gate of the transistor again. The bit pattern is thus erased and returned to the EPROM in its original state. The windowless OTPs can be deleted with X-rays, as they penetrate without windows through the housing and the block itself is the same except for the case.
A conventional quenching process takes about 10 to 30 minutes. Since the ionization after turning off the light source is not immediately subsided again and the blocks are heated depending on the type of extinguishing device using the allowable temperature for programming addition, the programming can be done only after a further waiting period. The times can be reduced significantly through the use of fire extinguishers with flash technology. Instead of continuous radiation while the blocks are subjected to several intense light flashes. If the specifications of the module manufacturer for the deletion are not followed correctly, a seemingly correct programming with shortened data life may be the result.
The quartz glass window should be protected after programming with an opaque label. An unprotected EPROM can be erased after 90 days of direct sunlight. The lighting of the memory cells with an ordinary photo flash can cause short-term data corruption and therefore computer failures.
A further development of the EPROM is electrically erasable EEPROM ( electrically erasable PROM) and the flash EEPROM. Flash EEPROMs have widely replaced the EPROMs from the market.
256KiBit EPROM in laser engraved ceramic case.
256KiBit EPROM in close-up with bond wires.
Due to the regular structure of memory cells are generated at the chip interference colors
Three soviet 2Ki x 8 EPROMs ( К573РФ2, КС573РФ2 ) and a M2716 by SGS.
Pin assignment
Like other integrated circuits are standardized by the JEDEC pinout in their gängingen the EPROM.
In-Circuit Simulation
Because EPROMs are not unlimited rewritable, simulators are used in the development phase of electronic devices. These are available in different variants. For example, there are simulators with a USB port, to simulate the EPROMs to 4 Mibit size. In these devices, the program code is loaded via USB to the simulator and the simulated EPROM inserted in the circuit construction such as a plug-in adapter. It can be started immediately with the simulation. The circuit under test behaves exactly as if a real EPROM chip was installed. One in existing EPROM programming device very cost effective solution offering even simple simulators from battery-backed RAM blocks with write protection switch that can be programmed at the EPROM programming device and then plugged with write protection is enabled on the test circuit.