Flash Qing Xu Tie Chen

Flash An electronic device Non-volatile Can be electrically erased and reprogrammed Usage: Digital Music Device Smartphones Digital Cameras Removable Storage Devices (picpedia.com)

Non-Volatile Memory Non-Volatile Memory in Embedded System: Stores data after power down – Battery Change – Consumer Electronics

Flash Non-Volatile Memory Read-Only: ROM Read-Write: EPROM, E 2 PROM, FLASH (Figure Credit: Prof. Dennis Sylvester)

Flash Flash Development vs. Moores Law (Figure Credit: H. Cho, Stanford University)

MOSFET How does a MOSFET transistor work? (Wikipedia - Threshold formation in MOSFET)

Flash How is Flash different from MOSFET? (Figure Credit: Prof. Grishman, CSCI Inc.)

Flash Operations Writes a Logic ZERO Writes a Logic ONE (Figure Credit: S. Verna, Stanford University)

Flash Wearing Erosion of a flash memory Programming and erasing breaks down the oxide layer in the transistor. Life of 100,000 Program/Erase cycles (Figure Credit: Prof. Li-Ping Zhang)

Flash Wearing Flash Memory Controller Arrange data so that programming/ erasing is distributed evenly A block of extended life memory is allocated for the controller, stores operation data. Flash Wear Leveling Algorithm: Dynamic Static

Flash Wear Leveling Dynamic Wear Leveling: - Controller selects new free data block before write - Mapping points to new block location after write Disadvantage: - Static blocks where data do not change (eg. OS file) wears slower than other blocks - Reduce lifespan of the flash drive

Flash Wear Leveling Static Wear Leveling: - Works the same as dynamic wear leveling - Static blocks that do not change are periodically moved Disadvantage: - Moving static blocks takes time

Flash Wear Leveling Dynamic vs. Static What to use? Use Both! StaticDynamic PerformanceSlowerFaster ComplexityMore ComplexLess Complex EnduranceLongerShorter

Introduction to AT45DB161D

Important Facts 4,096 Pages (512/528 Bytes/Page) Main Memory (2MB in total) Single 2.5V - 3.6V or 2.7V - 3.6V Supply SPI Serial Port Interface – Mode 0 and Mode 3 compatible Two SRAM Data Buffers (512/528 Bytes) 100,000 Program/Erase Cycles Per Page Minimum

Block Diagram (Figure Credit: AT45DB161D Datasheet)

Pin Configuration SymbolFunctionAsserted StateType CSnChip SelectLowInput SCKSerial Clock-Input SISerial Input-Input SOSerial Output-Output WPnWrite protectionLowInput RESETnResetLowInput RDY/BUSYnReady/BusyLowOutput VCC Device Power Supply -Power GNDGround-

SPI Interface A valid instruction starts with the falling edge of CS followed by the appropriate 8-bit opcode and the desired buffer or main memory address location.

Read Operations Main Memory Page Read Buffer Read Main Memory Page to Buffer Transfer (Figure Credit: AT45DB161D Datasheet)

Write Operations Buffer Write Buffer to Main Memory Page Program (Figure Credit: AT45DB161D Datasheet)

Erase Operations Page Erase (528/512 bytes) Block Erase (8 pages) Sector Erase (256 pages) Chip Erase (all 16 sectors, which is 2MB)

Modifying Data in Flash (Figure Credit: AT45DB161D Datasheet)

Why do We need Buffers? Because it saves us a lot of trouble! The minimum size of erase/programming is one page. You will have to send exactly one page data through SPI for every write operation without buffers. You may have to first send back one page data from flash even before that!

Timing Issues Erase and Program time Flash output delay Setup time, hold time of all serial port … You are able to find timing diagrams and characteristic tables in datasheet. (Figure Credit: AT45DB161D Datasheet)

Power Issues 7 mA Active Read Current Typical 12 mA Active Program/Erase Current Typical 25 μA Standby Current Typical 9 μA Deep Power Down Typical (Figure Credit: AT45DB161D Datasheet)

Other Features Software Sector Protection Sector Lockdown Status Register Security Register Deep Power-down and Resume Page Size Option

Reference introduction.html introduction.html S. Verma, Tunnel Barrier Engineering for Flash Memory Technology, Stanford University, May 2010 H. Cho, Low Power, Highly Scalable, Vertical Flash Memory Cell and MOSFET, Stanford University, Sept 2007 ATMEL, AT45DB161D 16-megabit DataFlash Specification L.P. Zhang, Low Cost Wearing Algorithm for Block Mapping Solid State Disks, National ChiaoTung University, Taiwan

Questions?