Shulou(Shulou.com)06/02 Report--

I. introduction to Flash 1. Development situation

two。 Compare the differences between 2.1RAM and ROM

RAM (random access memory, random access memory), characterized by arbitrary byte read and write, power loss

ROM (read only memory, read-only memory, similar to Flash SD card, etc.) is used to store things, power is not lost, can not be accessed by random address, can only be accessed in blocks

2.2 Magnetic storage and flash storage

Magnetic storage. Advantages: mature technology, low price; disadvantages: slow reading and writing speed, poor reliability, can not be used in embedded devices

Flash storage. Advantages: fast reading and writing speed and no physical loss

2.3MLC and SLC

SLC, the technology is relatively early, the reliability is high, the disadvantage is that the capacity is not large (or the capacity is too expensive, generally the SLC Nand is below 512MB)

MLC, the technology is relatively new, immature, poor reliability, the advantage is that the capacity can be done very large and cheap, now basically in the development of MLC technology

2.4nand and SD card, MMC card, MicroSD, TF card

Nand only makes the most basic read-write interface to the memory unit, and then requires the external SoC to provide Flash read-write controller to read and write timing with Flash. Defects: 1. The timing of the read-write interface is complex. 2. There is no internal bad block handling mechanism, so it is necessary for SoC to manage the bad blocks of Flash by itself; 3. The Flash interfaces of different manufacturers are inconsistent, and even the Flash interfaces of different models and series of the same manufacturer are inconsistent, which makes it very troublesome to upgrade products.

SD card has more unified external package and interface than direct Nand chip. All cards have a unified standard. For example, SD cards are issued in accordance with the SD specification. These specifications specify the read-write speed, read-write interface timing, read-write command set, card size, number of pins and definition of SD card. The advantage of this is that SD cards from different manufacturers can be universal.

2.5nand and iNand, MoviNand, eSSD and SD cards, etc.

SD card, external expansion card for a long time, the card slot may be unreliable due to poor contact.

Inand, advantages: 1, learn from SD card, there is a unified interface standard (including pin definition, physical packaging, interface timing). 2. Learn from the original Nand and release it on a chip instead of a card. 3. Built-in Flash management module provides functions such as bad block management, which makes the management of Nand easier.

2.6 differences between SD card and MicroSD,MMC,TF

MMC

(1) the standard is earlier than SD standard, and SD standard is compatible with MMC standard.

(2) the MMC card can be read and written by the SD reader, while the SD card cannot be read and written by the MMC reader.

MicroSD, the size is different, the transmission is exactly the same as the principle.

TF card

(1) in appearance, SD cards are large and TF cards are small; for purposes, SD cards are used in digital cameras, etc., while TF cards are widely used in mobile phones, GPS, etc.

(2) in terms of timing, the SD card was launched in 1999 and the TF card was launched in 2004; the SD card was jointly launched by Panasonic, Toshiba and SanDisk of the United States, while the TF card was jointly launched by Motorola and SanDisk.

(3) SD card has write protection but TF card does not. TF card can be converted into SD card through card holder.

Reference: Mr. Zhu's embedded course

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