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Author | strongerHuang
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Recently, I saw small partners in the exchange group discussing the topic of MCU Flash, such as: Flash type, speed, etc.
We usually encounter all kinds of Flash in the development process of single-chip microcomputer, such as: SPI Flash, Nor Flash, Nand Flash and so on.
Today I will simply share with you related content.
The development of Flash and the difference between NOR and NAD Flash
Flash, also known as Flash Memory, is usually referred to as "flash memory".
Flash combines the strengths of ROM and RAM, not only has the function of electronically erasable and programmable (EEPROM), but also can read data quickly, and has the advantages of NVRAM (NVRAM: Non-Volatile Random Access Memory, non-volatile random access memory).
In the past, embedded systems have always used ROM (EPROM) as their storage device. The emergence of Flash has completely replaced the status of ROM (EPROM) in embedded systems, used to store Bootloader and operating system or program code or directly as Hard disk use (U disk, solid state disk).
1.NOR Flash
Intel first developed NOR flash technology in 1988, which completely changed the situation where EPROM and EEPROM dominated the world.
The reading of NOR Flash is the same as that of our common SDRAM, that is, it can be read and written randomly according to the address, and users can directly run the code loaded in NOR FLASH, which can reduce the capacity of SRAM and save costs. Because of its fast reading speed, it is mostly used to store important information such as programs and operating systems.
2.NAND Flash
In 1989, Toshiba released the NAND flash structure, emphasizing the reduction of cost per bit, higher performance, and it can be easily upgraded through the interface like a disk.
NAND Flash does not adopt the random read technology of memory. It reads one block at a time, usually 512 bytes at a time. The cost of making Flash with this technology is cheaper.
Users cannot directly run the code on NAND Flash, so many development boards that use NAND Flash use a small NOR Flash to run the startup code in addition to NAND Flash.
3. Compare
Compared with NOR Flash, NAND Flash has better writing performance and lower cost under large capacity.
At present, the Flash Memory used in most mobile phones, tablets, SD cards, solid-state drives and other devices belongs to NAND Flash.
Is the MCU Nor or Nand Flash?
Flash is mainly divided into Nor Flash and Nand Flash.
In addition to our common (parallel) Nor Flash and Nand Flash chips, in fact, SPI Flash chips are also divided into SPI NOR Flash and SPI NAND Flash chips, and you can find their classification in many official sellers of SPI Flash.
Back to the topic of this article: Is the Flash inside the MCU Nor or Nand Flash?
We use external program storage chips, mainly NOR Flash. Have you ever seen anyone using Nand Flash to run programs?
Several reasons why Nand Flash is not suitable for running programs:
1. The address cannot be accessed randomly;
2. There are bad blocks, which are not suitable for storing programs;
3. In the process of repeated reading for a long time, the data in Nand is relatively less stable than Nor;
Therefore, the internal Flash of the microcontroller is usually Nor Flash .
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