* In order to facilitate understanding and save the trouble of capacity unit conversion , The following capacity units are used Byte Company （128Mbit=16MByte）

　　 Preface ：

　　NOR FLASH It is one of the two main nonvolatile flash memory technologies in the market .Intel On 1988 First developed in NOR Flash technology ( In fact, it was first developed by Toshiba's Fujitsu ), Completely changed the original by EPROM(Erasable Programmable Read-Only-Memory Electrically programmable read only memory ) and EEPROM( Electrically erasable read only memory Electrically Erasable Programmable Read - Only Memory) The situation of the rule of the world . Then ,1989 year , Toshiba has published NAND Flash structure , Emphasis on reducing the cost per bit , It has higher performance , And like a disk, it can be easily upgraded through the interface .NOR Flash It is characterized by on-chip execution （XIP ,eXecute In Place）, In this way, the application can directly in Flash Running in flash memory , You don't have to read the code into the system RAM in .NOR High transmission efficiency , stay 1~4MB High cost-effectiveness at low capacity , But the low write and erase speed greatly affects its performance .NAND The structure can provide extremely high cell density , High storage density , And the speed of writing and erasing is very fast . application NAND The difficulty is that Flash The management of requires special system interfaces . Usually read NOR Faster than NAND Faster , and NAND Write speed ratio of NOR Much faster , These situations should be considered in the design .

　　 Text ：

　　 With the rise of the Internet of things ,MCU The application of is also more and more extensive , In the past, it was basically built-in EEPROM Or external small capacity NOR Flash Can meet most of the needs , With the development of technology and the improvement of application requirements , gradually MCU More and more functions need to be realized , While realizing more functions, the amount of data that needs to be stored is also increasing , For example, the system increases 、 Store audio 、 picture （GUI）、 Video cache 、 Protocol stack, etc …

　　 In general NOR FLASH When the capacity is not enough, the users of are directly upgraded to a higher level of capacity NOR FLASH That's all right. , However, there are two general situations , because NOR The reason for the relatively large unit structure of , When the capacity reaches a certain level, the cost performance will be abnormally low , Combined with the production process and the current market situation ,16MB It's a watershed , Than 16MB NOR Flash A big one 32MB NOR Flash The price of is relative to 16MB NOR Flash A lot higher , Even better than 128MB Of NAND Flash Even more expensive , To make matters worse, the supply of the goods is still poor , Even if you can accept 32MB NOR Flash And developed the scheme , The preliminary commissioning and trial production have passed , When it comes to formal mass production, it will not arrive … You may miss the best time to sell the whole machine .

　　 At this time, someone will say ： I know all this ！ I also want to use NAND Flash ah ！ But my MCU No ！ the ！ a ！NAND Flash ah ！ Is it difficult? I have to change the platform and redevelop from scratch ？

　　 no , This time is different from the past , There's a man named SD NAND You can choose from ,NAND framework 、SD agreement , As long as it's support SD2.0 Agreed MCU Can be used . Use under normal circumstances SPI Pattern , If you need faster speed and IO It can be used when the mouth is enough SD Pattern . built-in ECC、 Bad block management 、 Balanced erasure and other functions , This means that users do not need additional write drivers to manage NAND , Of course, the performance is weak MCU I can't do it ^^

　　SD NAND For more information, please refer to the following article

　　 Portal :  Technical Q & A - What is? SD NAND？ (longsto.com)

　　 because SD NAND The storage unit uses NAND framework , therefore NAND The basic characteristics of holding have also been inherited ,SD NAND Further optimization has been made on this basis , It greatly improves usability and application compatibility .

　　 Let's take a look first NOR And NAND What are the differences .

　　1.NOR Flash Support random access , So support XIP(execute In Place),NAND Flash Need to read by block , So I don't support XIP .

　　2.NAND FLASH Theoretical reading speed vs NOR Flash Close , The actual situation will vary according to different interfaces .

　　3.NOR And NAND Erase before writing ,NOR Erase with 64～128KB Block of , Perform a write / The erase operation takes about 5s,NAND Erase with 8～32KB Block of , Perform a write / The erase operation takes about 4ms.

　　4.NAND Theoretical maximum erasure ratio NOR many

　　5.NOR Drive ratio NAND Simple ,NAND FLASH It needs to be done through special NFI（NAND FLASH Interface） And Host End to end communication , The drive is relatively complex .

　　6. all Flash There will be bit inversion ,NAND The probability of bit reversal is higher than NOR high ,NAND Flash You have to use ECC.

　　7.NAND The unit size of is almost NOR Half of the device , therefore NAND A lower cost .

　　 summary ： NOR And NAND Each has its own characteristics , Application scenarios and application difficulties are also different ,SD NAND  In keeping with NAND Improve the deficiencies while building high-quality features , The built-in controller can manage itself NAND Flash, Users do not need to deal with it externally ECC And bad block management , Save it. MTD layer , Users do not need to write tedious driver code . These features also make NOR User upgrade NAND Make it possible .

　　 Insert ads ^^：CS Genesis now offers 128MB,512MB,4GB Equal capacity , Both commercial and industrial grade options are available , Users can choose according to their own needs .

　　128MB Details page ：128MB SD NAND

　　PS.  except SD NAND  There is also a secondary upgrade scheme , That's using TF card , However, this solution depends on the specific application environment .SD NAND And TF For card comparison materials, please refer to the following articles , I hope you can find your own products .

　　 Portal ：SD NAND And TF The difference between cards - Technical Q & A (longsto.com)