Detailed knowledge of EEPROM principle

EEPROM (Electrically Erasable Programmable Read-Only Memory), a memory chip that does not lose data after power-down. The EEPROM can erase existing information and reprogram it on a computer or on a dedicated device. Generally used in plug and play. The EEPROM (Electrically Erasable Programmable Read Only Memory) is a user-readable read-only memory (ROM) that can be erased and reprogrammed (overwritten) by acting above a normal voltage. Unlike EPROM chips, EEPROMs can be modified without being removed from the computer. In an EEPROM, the life of the EEPROM is an important design consideration when the computer is frequently reprogrammed when in use.

Generally used for Plug & Play; commonly used in interface cards to store hardware settings data; also commonly used in "hardware locks" to prevent illegal copying of software. EEPROM-Background In the early days of the development of the microcomputer, the BIOS was stored in a ROM (Read Only Memory). The internal data of the ROM is burned in a special way in the manufacturing process of the ROM. The contents of the ROM can only be read and cannot be changed. Once it is burned in, the user can only verify whether the written data is correct. No further modifications can be made. If you find any errors in the data, you can only make a copy if you don't use it. ROM is produced on the production line and is generally used only in high-volume applications due to its high cost. Due to the inconvenience of ROM manufacturing and upgrading, a PROM (Programmable ROM) was later invented. Initially, there is no data inside the PROM made in the factory. The user can write his own data with a dedicated programmer, but this opportunity is only once. Once it is written, it cannot be modified. If an error occurs, it is written. The chip can only be scrapped. The characteristics of the PROM are the same as those of the ROM, but the cost is higher than that of the ROM, and the speed of writing data is slower than that of the ROM. Generally, it is only suitable for a small number of occasions or for pre-production verification of the ROM. The EPROM (Erasable Programmable ROM) chip can be repeatedly erased and written, which solves the drawback that the PROM chip can only be written once. The EPROM chip has a very obvious 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 erased 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 certain programming voltage must be added when writing content to the chip (VPP=12-24V, depending on the chip model). The EPROM model starts with 27, such as 27C020 (8*256K) is a 2M Bits capacity EPROM chip. After writing the data, the EPROM chip also seals the window with an opaque sticker or tape to protect the data from the surrounding ultraviolet rays. EEPROM - Basic Principles Due to the inconvenience of EPROM operation, most of the BIOS ROM chips on the motherboard are EEPROM (Electrically Erasable Programmable ROM). The EEPROM eraser does not need to resort to other devices. It modifies its contents with electronic signals, and uses Byte as the minimum unit of modification. It is not necessary to wash all the data to write, completely eliminating the EPROM Eraser and the programmer. Bondage. When the EEPROM writes data, it still needs to use a certain programming voltage. At this time, it is easy to rewrite the content by using a dedicated refresh program provided by the manufacturer. Therefore, it belongs to a dual voltage chip. By means of the dual voltage characteristic of the EEPROM chip, the BIOS can have a good anti-virus function. When upgrading, the jumper switch is turned to the "ON" position, that is, the corresponding programming voltage is added to the chip, and the upgrade can be conveniently performed; When used normally, the jumper switch is turned to the "OFF" position to prevent illegal modification of the BIOS chip by the CIH virus. Therefore, many motherboards still use EPROM as a BIOS chip and have become a major feature of their motherboards.