EPROM is a ROM memory that has an erasable function and can be reprogrammed after erasing. Before writing, the content must be cleared by ultraviolet light to illuminate the transparent window on its IC card. This type of chip is relatively easy to identify, and its package contains “quartz glass window”. A “quartz glass window” of a programmed EPROM chip is generally covered with black self-adhesive paper to prevent direct sunlight.
EPROM chip can be repeatedly erased and written
It solves the drawback that the PROM chip can only be written once. The EPROM chip has an unusual feature. On the ceramic package on the front side, a glass window is opened through which the integrated circuit can be seen. The ultraviolet light can be wiped through the hole to illuminate the internal chip. The internal data, the EPROM eraser, is used to complete the chip erase operation. The writing of the data in the EPROM requires a dedicated programmer, and a specific programming voltage must be added to the contents of the chip (VPP=12~24V, depending on the chip type). The EPROM model starts with 27, such as 27C020 (8*256K) is a 2M Bits capacity EPROM chip. After the EPROM chip is written, the window is sealed with an opaque sticker or tape to protect the data from the surrounding ultraviolet rays. When the EPROM chip is in the new state (after being erased by ultraviolet light), the data of each internal memory cell is 1 (high level) Note: 0 is low level .
Programming of the EPROM requires the use of a EPROM programmer. The programmer is the device used to generate the high voltage pulse signals as are necessary for EPROM programming. When programming, the EPROM data is sent to the random memory, and then the programming program is started, and the programmer writes the data to the EPROM line by line.
A piece of programmed EPROM can hold its data for about 10 to 20 years and can read indefinitely. The erase window must remain covered to prevent accidental erasure by sunlight. Older computer BIOS chips are generally EPROMs, and the erase window is often overwritten with the label of the BIOS publisher’s name, version, and copyright notice. The EPROM has been replaced by an EEPROM (Electrical Erasing Read-Only Register).
Some microcontrollers produced before the appearance of flash memory use EPROM to store the version of the program for program development; such as the use of one-time programmable devices, it will cause dangerous waste during debugging .
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