Introduction to the basic concepts of NAND Flash

I. Pin Introduction

Pin name	Pin Function
CLE	Command lock function
Ale	Address lock function
/CE	Chip enabling
/Re	Read enabling
/We	Write enable
/WP	Write Protection
R/B	Ready/busy output signal
VCC	Power Supply
VSS	Location
N. C	Not connected
Io0 ~ Io7	Transmit data, commands, and addresses

1. commands, addresses, and data are transmitted through eight I/O Ports. when writing commands, addresses, and data, we and Ce signals must be lowered at the same time. data is locked by NAND flash on the rising edge of the we signal. 4. command lock signal CLE and address lock signal ale are used to distinguish, lock command or address 5. on the rising edge of CLE, the command is locked. 6. on the rising edge of ale, the address is locked

Ii. Storage Organization

1. the NAND chip contains die, plane, block, and page 2. chip refers to the chip. an encapsulated chip is a chip 3. die is a small square on a wafer. Several die may be encapsulated in a chip. Due to different flash technologies and different technologies, the concept of die is generated. Mono die is a common concept, A die, B die, etc. A chip contains N die 4. plane is the smallest unit for NAND to operate based on commands such as read, write, and erase.

A plane is a storage matrix that contains several blocks.

5. Block is the minimum erasure unit of nandflash. A block contains several pages. 6. The page is the minimum read/write unit of nandflash. A page contains several bytes.

OOB/spare Area

Each page has a corresponding area called sparearea ). In Linux, it is generally called OOB (out of band ).

Data Reading and writing are relatively prone to errors. To ensure data correctness, a corresponding detection and correction mechanism is required. This mechanism is called Ecc/EDC, so redundant areas are designed, the check value used to store data.

OOB reads and writes are completed along with page operations.

OOB has the following functions:

? Indicates whether the block is a bad block.

? Store ECC data

? Stores data related to file systems. For example, jaffs2 will use these spaces to store some specific information, while the yaffs2 file system will store a lot of information related to its own file system in OOB.

The storage structure of a 16 gb nand is roughly as follows:

A 16 GB nandflash requires a 34-bit address, while the I/O port of the transmission address is 8-bit. Therefore, it requires five loops to transmit address information.

Bad Block in NAND Flash

In NAND Flash, one block contains one or more digits, which is called Bad block. The stability of Bad blocks cannot be guaranteed.

That is to say, you cannot guarantee that the data you write is correct or that the data you write is correct. Reading is not necessarily correct. The corresponding normal block, certainly

It is normal to write and read data.

There are two types of Bad blocks:

(1) There are bad blocks at the factory:

One is that when you leave the factory, that is, the new NAND flash you have bought can contain Bad blocks. This type of bad block is known as factory (masked) Bad block or initial bad/invalid block, which will be marked before the factory is released,

It is marked as a bad block.

(2) Bad blocks generated during use:

The second type is generated during the use process. Because the use process takes a long time, an error occurs when the block is erased. This indicates that the block is broken.

It must be found during the running of the program and marked as bad blocks. The location of the tag. This type of block is called worn-out.

Bad block. That is, a broken block is used.

Implementation Mechanism of SLC and MLC

Nandflash can be divided into SLC and MLC Based on the voltage levels of the internal storage data unit, that is, whether one-bit data or multiple-digit data is stored in a single memory unit.

? SLC (single level cell)

A single storage unit only stores 1 bit, indicating 1 or 0.

For NAND Flash write 1, it is to control externalgate to charge, so that there is enough storage charge, exceeding the threshold Vth, it indicates 1.

For write 0, it is to discharge it, the charge is reduced to less than Vth, it indicates 0

? MLC (multi level cell)

It corresponds to SLC, that is, a single storage unit can store multiple places, such as two or four places. The implementation mechanism is to control the internal charge

Is divided into multiple thresholds to store different data.

A single storage unit can store 2-bit data, called 2 to the power of 4 levelcell

Introduction to the basic concepts of NAND Flash