EEPROM (live erasable programmable read only memory) is a user changeable read only memory (ROM), which can be erased and reprogrammed (rewritten) by higher than normal voltage. Unlike EPROM chips, EEPROM can be modified without taking it out of the computer. In an EEPROM, when the computer is in use, it can be programmed frequently, so the life of EEPROM is a very important design consideration parameter. EEPROM is a special form of flash memory. Its application is usually the voltage in personal computer to erase and reprogram
EEPROM is generally used for plug & play.
It is commonly used in the interface card to store hardware setting data.
It is also commonly used in the “hardware lock” to prevent illegal copying of software.
Difference between EEPROM and EPROM
1、 The development history of EEPROM and EPROM is different
In the early stage of microcomputer development, BIOS was stored in ROM. the data inside ROM was burned in the ROM manufacturing process in the factory with special methods. The content can only be read and cannot be changed. Once burned, the user can only verify whether the written data is correct and can not make any modification. If any error is found in the data, it can only be discarded. Due to the inconvenience of ROM manufacturing and upgrading, prom was invented later. There is no data in the prom originally made in the factory. Users can write their own data with a special programmer, but this opportunity is only once. Once written, it cannot be modified. If there is an error, the written chip can only be scrapped. Prom has the same characteristics as ROM, but its cost is higher than ROM, and the speed of writing data is slower than that of ROM mass production. Generally, it is only suitable for occasions with small demand or verification before ROM mass production.
EPROM chip can be erased and written repeatedly, which solves the disadvantage that Prom chip can only be written once. EPROM chip has an obvious feature. A glass window is opened on the ceramic package on its front. Through this window, you can see the integrated circuit inside. Ultraviolet light shines through the hole, and the data inside the chip can be erased. EPROM eraser is used to complete the operation of chip erasure. After the EPROM chip writes the data, the window should be sealed with an opaque sticker or adhesive tape to avoid damage to the data caused by the surrounding ultraviolet radiation. EPROM programming needs to be completed by programmer. The programmer is a device for generating high-voltage pulse signals required for EPROM programming. When programming, the EPROM data is sent to the random access memory, and then the programming program is started, and the programmer writes the data into EPROM line by line. A programmed EPROM can keep its data for about 10 to 20 years and can be read indefinitely. The erase window must remain covered to prevent accidental erasure by sunlight. The BIOS chip of old computers is generally EPROM, and the erase window is often covered by the label printed with the name, version and copyright notice of the BIOS publisher. EPROM has been replaced by EEPROM.
Due to the inconvenience of EPROM operation, most of the BIOS ROM chips on the motherboard later adopted EEPROM. The erasure of EEPROM does not need the help of other devices. It uses electronic signals to modify its content, and takes byte as the minimum modification unit. It does not have to wash all the data to write, completely getting rid of the constraints of EPROM, eraser and programmer. When EEPROM writes data, it still needs to use a certain programming voltage. At this time, it can easily rewrite the content by using the special refresh program provided by the manufacturer. With the help of the dual voltage characteristics of EEPROM chip, the BIOS can have good anti-virus function. When upgrading, turn the jumper switch to the “on” position, that is, add the corresponding programming voltage to the chip, and it can be upgraded conveniently; When in normal use, turn the jumper switch to the “off” position to prevent CIH viruses from illegally modifying the BIOS chip.
2、 Performance difference between EEROM and EPROM
EPROM is a rewritable memory chip, and its contents will not be lost when power is off. It is nonvolatile. It is programmed by EPROM programmer, which can provide a higher voltage than the normal working voltage to program EPROM. Once programmed, EPROM can be erased only under strong ultraviolet radiation. In order to erase, the ceramic package of EPROM has a small quartz window. Generally, the quartz window is covered with opaque adhesive tape. When erasing, remove the adhesive tape, and then place it under strong ultraviolet light for about 20 minutes.
EEPROM is an electrically erasable programmable read-only memory, and its contents will not be lost in case of power failure. Under normal circumstances, EEPROM is read-only like EPROM. When writing is required, it can be written or erased by adding a high voltage to the specified pin, and its erasure speed is very fast. Generally, EEPROM chips are divided into Serial EEPROM and parallel EEPROM. When reading and writing, the data input / output of Serial EEPROM is carried out through 2-wire, 3-wire, 4-wire or SPI bus, while the data input / output of parallel EEPROM is carried out through parallel bus.
3、 Application difference between EEPROM and EPROM
For a small system that needs switch setting parameters, parameters such as baud rate, synchronous and asynchronous selection, data length and so on can be stored in EEPROM to formulate a data sequence or table, so that users can easily complete the selection. Each time the CPU is powered on, the specified working mode is set according to the parameters set in EEPROM. For large-scale computers and communication networks, control information such as channel configuration, data rate and bearing capacity of the terminal can be displayed on the CRT in the form of tables. The system can be easily configured on the CRT. EEPROM can store these data and tables well, which solves the problems of stability and flexibility of the communication network.
EPROM is a common memory. It is generally used as program memory in the development and application of single chip microcomputer. In fact, it is also a programmable logic device. In addition to realizing the logic function, it can also be used to realize some complex measurement and control. The usual digital voltmeter adopts liquid crystal display, the display brightness is not high, and the display number is not large. This paper introduces a large display LED digital DC voltmeter with a / D converter and EPROM as the core. It is suitable for teaching experiment demonstration, instrument panel and cabinet of measurement and control equipment.