General differences between EEPROM, EPROM, and Flash

Both EEPROM, EPROM, and FLASH are based on a Floating gate transister structure. The Floating gate of the EPROM is in an insulating silica layer, and the charged electrons can only be stimulated by ultraviolet energy. The EEPROM unit is FLOTOX (Floating-gate tuneling oxide transister) and an additional Transister, because of the characteristics of FLOTOX and two-tube structure, it can be read/written in a single element. Technically, FLASH is achieved by combining EPROM and EEPROM technology. Many FLASH uses avalanche hot electronic injection to program FLASH, which can be erased and used in the same way as EEPROM.
Fowler-Nordheim tuneling. However, the main difference is that FLASH can erase large blocks or whole blocks of the chip, which reduces the design complexity and does not need the redundant Tansister In the EEPROM unit, so it can achieve high integration, large capacity, and the floating gate technology of FLASH is also different, the write speed is faster.

In fact, the main difference between EEPROM and FLASH is

1. The EEPROM can be wiped by bit, while FLASH can only wipe a large part.

2. Generally, the size of the EEPROM is not large. If it is large, the EEPROM is relative to the FLASH
There is no price advantage. The EERPOM of stand alone sold on the market is generally under 64 KBIT, while FLASH is generally above 8 Meg BIT (NOR type ).

3. The reading speed should not be the difference between the two, but EERPOM is generally used for low-end products. The reading speed does not need to be so fast. If you really want to do it, you can actually do the same as FLASH.

4. Because the storage unit of EEPROM is two tubes and FLASH is one (except for SST, similar to two tubes ),
It's better. It's okay if it's times.

In general, there is no big difference between EEPROM and FLASH, but EEPROM is a low-end product with low capacity and low price, but its stability is better than that of FLASH.

But for the design of EEPROM and flash, Flash is much more difficult, either from the process or from the peripheral circuit design.

Flash Memory refers to "Flash Memory", the so-called "Flash Memory", which is also a non-volatile memory and belongs to the improved product of EEPROM. Its biggest feature is that it must be erased by block (the size of each block is not fixed, and products of different manufacturers have different specifications ), the EEPROM can only erase one byte at a time ). Currently, "Flash Memory" is widely used on the motherboard of a PC to save BIOS programs and facilitate program upgrade. Another major application area of Ram is used as a replacement for hard disks. It has the advantages of earthquake resistance, fast speed, no noise, and low power consumption. However, it is not suitable to replace RAM with it,
Because Ram needs to be able to rewrite in bytes, Flash ROM cannot.

Rom and RAM are both semiconductor memory, Rom is short for read only memory, and Ram is short for random access memory. ROM can still maintain data when the system stops power supply, while Ram usually loses data after power loss. A typical Ram is the computer memory.
Ram has two categories: static RAM (static RAM/SRAM). The speed of SRAM is very fast. It is the fastest storage device for reading and writing, but it is also very expensive, so it is only used in demanding places, such as the first-level buffer of the CPU and second-level slow flushing. The other is dynamic RAM (Dynamic RAM/Dram). DRAM retains data for a short period of time and is slower than SRAM, but it is faster than any Rom, but in terms of price, DRAM is much cheaper than SRAM, and computer memory is dram.
DRAM is divided into many types. Common types include fpram/fastpage, edoram, SDRAM, ddr ram, RDRAM, sgram, and wram. Here we will introduce a ddr ram. Ddr ram (date-rate RAM) is also called ddr sdram. The improved Ram is basically the same as that of SDRAM. The difference is that it can read and write data twice at a clock, this doubles the data transmission speed. This is the most widely used memory in computers, and it has a cost advantage. In fact, it beat Intel's other memory standard-Rambus DRAM. High-speed DDR is also available on many high-end video cards.
Ram to increase the bandwidth, which can greatly improve the pixel rendering capability of the 3D accelerator card.
There are also many types of Rom. The difference between the prom and the EPROM is that the prom is one-time, that is, after the software is filled in, it cannot be modified. This is an early product and cannot be used now. The EPROM is used to erase the original program through ultraviolet radiation and is a general memory. Another type of EEPROM is to be wiped out by an electronic device. It has a high price, a long write time, and a low write speed.
For example, the mobile phone software is usually placed in the EEPROM. When we call, some of the last dialing numbers are temporarily stored in the SRAM, rather than writing the pass record immediately (the call record is stored in the EEPROM ), at that time, there was a lot of important work (CALLS) to do. If you write data, a long wait would be unbearable for users.
Flash Memory, also known as flash memory, combines the strengths of ROM and Ram, not only has the electronic Erasable Programmable (EEPROM) performance, data will not be lost after power failure, and data can be quickly read (NVRAM advantage), which is used in USB flash drives and MP3. In the past 20 years, embedded systems have been using ROM (EPROM) as their storage devices. However, in recent years, Flash has completely replaced the position of RoM (EPROM) in embedded systems, it is used to store bootloader, operating system or program code, or directly used as a hard disk (USB flash disk ).
Currently, there are two types of FLASH: nor flash and nadn flash. The reading of nor flash is the same as that of our common SDRAM. Users can directly run the code loaded in nor flash, which can reduce the capacity of SRAM and save costs. NAND Flash does not adopt the random read Technology of memory. It reads 512 bytes at a time, usually in a low cost. Users cannot directly run code on NAND Flash. Therefore, in addition to using NAND flah, many development boards that use NAND Flash also provide a small nor
Flash to run the startup code.
NOR Flash is usually used for small capacity. Because of its fast reading speed, it is used to store important information such as the operating system, while nand flash is used for large capacity, the most common nand flash application is the DOC (Disk On Chip) used in the embedded system and the "FLASH Disk" we usually use, which can be erased online. FLASH on the market is mainly from Intel, AMD, Fujitsu and toshba, while the main manufacturers of NAND Flash are Samsung and toshba.
Speaking of SRAM, DRAM, and SDRAM
Static Random Access Memory is a type of semiconductor Memory. "Static" means that data stored in SRAM will not be lost if no power is lost. Unlike dynamic RAM (DRAM), DRAM requires periodic refresh operations. Then, we should not confuse SRAM with read-only Memory (ROM) and Flash Memory, because SRAM is a kind of volatile Memory, it can maintain data only when the power supply is continuously supplied. "Random Access" means that the content of the memory can be accessed in any order, regardless of the location of the previous access.
Each bit in the SRAM is stored in four transistors, which form two cross-coupled backbones. This storage unit has two stable states, usually 0 and 1. In addition, two access transistor s are required to control access to the storage unit during read or write operations. Therefore, a storage space usually requires six Enis. The symmetric circuit structure makes the access speed of SRAM faster than that of DRAM. Another reason why SRAM is faster than DRAM access is that it can receive all the address bits at a time, while DRAM uses a line address and column address multiplexing structure.
SRAM should not be confused with SDRAM, which represents Synchronous DRAM, which is totally different from SRAM. It should not be confused with PSRAM. PSRAM is a DRAM disguised as SRAM.
From the transistor type, SRAM can be divided into bipolar and CMOS. In terms of functions, SRAM can be divided into asynchronous SRAM and synchronous SRAM (SSRAM ). Asynchronous SRAM access is independent of the clock, and data input and output are controlled by address changes. All accesses to the synchronized SRAM are started along the rise/fall of the clock. Address, data input, and other control signals are related to clock signals.

(1) read-only memory (ROM) is a kind of semiconductor memory, which is characterized by the inability to change or delete data once stored. It is usually used in electronic or computer systems that do not need to change data frequently. The data will not disappear because the power supply is off. For example, early PCs such as Apple II or ibm pc xt/at boot programs (operating systems) or firmware in various other microcomputer systems ). Only Solid-state semiconductor memory with data stored in advance can be read. Rom. The data stored in ROM is generally written in advance before it is loaded into the entire machine. The entire machine can only be read during operation, rather than being quickly and conveniently rewritten as in random memory. The data stored in ROM is stable, and the data stored after power-off will not change. Its structure is simple and easy to read, so it is often used to store various fixed programs and data. In addition to a few types of read-only memory (such as character generator), the content of read-only memory varies with users. To facilitate usage and mass production, programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), and electroerasable programmable read-only memory (EEPROM) are further developed ). The EPROM can be erased only after a long time of ultraviolet radiation, which is inconvenient to use. The eeprom manufactured in 1980s overcomes the limitations of the EPROM, but the integration is not high and the price is higher. As a result, a new storage unit structure similar to EPROM flash memory was developed. Because of its high integration, low power consumption, small size, and fast online erasure, it has developed rapidly and may replace the existing hard disk and floppy disk and become the main large-capacity storage media. Most read-only memory is made of metal-oxide-Semiconductor (MOs) Fet. (2) Flash ROM: Flash memory, which is essentially an EEPROM-Electrically Erasable read-only memory. In general, Flash ROM and EPROM are not allowed to be written, you can add a high voltage to write or erase data. Therefore, maintenance and upgrade are convenient. The program disk for BIOS upgrade is generally provided by the motherboard manufacturer or can be downloaded from the Internet. To prevent system paralysis caused by accidental deletion of Flash BIOS content, General motherboard manufacturers have fixed a small boot block in Flash BIOS) it is used to take over the startup of the system in an emergency.