Flash Memory and Micro SD Card
Krishna Goyal (200601195) Anirudh Tripathi (200601141)
OUTLINE • • • • • • •
Memory Volatile and Nonvolatile memory EPROM and EEPROM memory Flash memory NAND and NOR Flash memory Flash Memory operations Advantage and Disadvantage of Embedded Over Stand Alone Flash Memory • Micro SD card • Summary • References
Memory • The terms “storage” or “memory” refer to the parts of a digital computer that retain physical state (data) for some interval of time, possibly even after electrical power to the computer is turned off. • A computer system's memory is crucial to its operation; without memory, a computer could not read programs or retain data. Memory stores data electronically in memory cells contained in chips. It is usually measured in kilobytes, megabytes, or gigabytes. • Memory is classified into volatile and non-volatile memory.
Memory Classification VOLATILE
EPROM EEPROM NVRAM Flash Memory Floppy Disk
Volatile Memory • The most widely used form of primary storage today is a volatile form of random access memory, meaning that when the computer is shut down, anything contained in random access memory (RAM) is lost. • DRAM used for main memory • SRAM used for cache
Non-Volatile memory • EEPROM, EPROM, FeRAM, FLASH, NVSRAM and ROM are different types of non-volatile memory. • The main differences are in the memories relative cost per bit and the flexibility to accommodate code changes. • nonvolatile memory, NVM or non-volatile storage, is computer memory that can retain the stored information even when not powered.
EPROM • Erasable Programmable Read Only Memory also known as UV-EPROM is a form of non-volatile memory. It is programmed electrically at high voltage using a charge that is injected into the floating gate. Data is erased by exposing the EPROM to UV light. The memory chip may then be reprogrammed with new data. • EPROMs are expensive because of the special quartz window packaging required for erasing capability. EPROMs are quickly being replaced by FLASH memory devices.
EEPROM • (Electrically Erasable Programmable ROM) A rewritable memory chip that holds its content without power. EEPROMs have a lifespan of between 10K and 100K write cycles, which is considerably greater than the EPROMs that came before them. • Unlike E-PROMs, which have to be placed under UV light for erasure, EEPROMs are erased in place. They use a floating gate to hold a charge like an E-PROM and have a second transistor for erasure.
Flash Memory • Flash memory is a programmable, read-only, nonvolatile memory similar to EPROM and EEPROM. Although flash memory is a derivative of EPROM and EEPROM. • EEPROM is automatically erased before a WRITE on a byte basis. Flash is either erased in blocks or the entire chip at once. • Flash memory is made of either NOR or NAND gates.
Flash Memory • Flash memory is used in memory card and flash drives to transfer data. • They are removable and re-writable and are much shorter than floppy disk and hold more information. • Flash memory is used in devices as cameras , mobile phones and video games. • Examples:-BIOS chip, compact flash, Smart media, Memory stick, Memory card.
Flash Memory Cell
Memory Architecture Diagram
USB Flash Drive
NAND and NOR Flash Memory • NOR flash supports random access and is used for instruction storage and execution known as "execute in place" (XIP). With a lifespan of about 100K write cycles, erasing and writing take several seconds, but reading is fast. • NAND flash, developed by Toshiba, reads and writes sequential, disk sector-sized blocks of 512 bytes, but must be erased in blocks from 16KB to 128KB. Less expensive than NOR, NAND flash can be rewritten up to a million times. Writing and erasing NAND flash is also faster than NOR.
Flash Memory Operation • Flash memory stores information in an array of floating gate transistors, called "cells", each of which traditionally stores one bit of Information • Newer flash memory devices, sometimes referred to as multi-level cell devices, can store more than 1 bit per cell, by using more than two levels of electrical charge, placed on the floating gate of a cell
Flash Memory Operation • Most modern NOR flash memory components are divided into erase segments, usually called either blocks or sectors. • All of the memory cells in a block must be erased at the same time. • Programming in NOR , generally performed one byte or word at a time.
NAND vs. NOR • NAND's advantages are fast write (program) and erase operations, while NOR's advantages are random access and byte write capability • NOR's random access ability allows for execute in place (XiP) capability, which is often a requirement in embedded applications
NAND vs. NOR • The disadvantages for NAND are slow random access, while NOR is, its slow write and erase performance. • The real benefits for NAND are faster program and erase times, as NAND provides over 5 Mbytes/s of sustained write performance. • The block erase times are 2 ms for NAND and 700 ms for NOR. • Clearly, NAND has several significant positive attributes. • However, it's not well-suited for direct random access.
Advantage of Embedded Over Stand-Alone Flash Memory • • • • • •
Higher System Speed Lower Power Higher Reliability Improved Security System-On-Chip(SOC) Capability Lower System Cost
Disadvantage of Embedded Over Stand-Alone Flash Memory • • • •
Single Source Increased Process Complexity Increased Test Cost Density Limitation
Introduction to Micro SD Card • MicroSD card is the memory card that is small and thin with SDMI(Secure Digital Music Initiative). • It is Flash based memory card designed to meet security, capacity, performance and environment requirements inherent to used in emerging audio and video electronic devices. • One of the great advantages of the Micro SD Cards is that they are backward compatible with many electronic devices that use standard SD memory cards.
Micro SD Card Interface Description
Features • Performance • Data Transfer Rate Read up to 23 MB/sec (Max) • Data Transfer Rate Write up to 20 MB/sec (Max)
Features • Add microSD card adapter can be use in SD card socket. • Support CPRM code. • No external programming voltage required. • SD card protocol compatible. • Correction memory field errors. • Easy handling for end user.
SD/SPI Bus Comparison microSD card using SD bus • Six wire communication channel( clock, command, 4 data lines) • Error protected data transfer • Single or multiple block oriented data transfer.
microSD card using SPI bus • Three wire serial data bus ( clock, dataIn, dataOut)+ card specific CS signal(hard wired card selection) • Optinal non protected data transfer mode available. • Single or multiple block oriented data transfer.
MicroSD card pinpout SD mode
MicroSD card pin out SPI mode
Summary • Flash technology is constantly changing, providing faster program and erase cycles, a bigger number of guaranteed erase and re-program cycles and longer data retention. Flash technology put on-chip with microcontrollers has now reached the point, where the in-application usability greatly improved. • In the past, storing of configuration data that stays available after a power-down and power-up cycle required an additional EEPROM or other storage device. Today, this functionality can be provided by on-chip Flash, further decreasing the parts count of embedded applications: an additional external EEPROM or SRAM might not be required anymore.
References • http://www.puremobile.com/flash-memorycards.asp • http://www.esacademy.com/faq/docs/flash/index.ht m • http://electronics.howstuffworks.com/flashmemory.htm • http://en.wikipedia.org/wiki/Flash_memory • http://www.dharmanitech.com
References • Paolo Cappelletti, Carla Golla, Piero Olivo, Enrico Zanoni “Flash Memories”, Kluwer Academic Publishers. • Joe E. Brewer and Manzur Gill “Nonvolatile Memory Technologies with Emphasis on Flash ”, Wiley Interscience