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In the past, flash-memory-memory parts were not much different from EPROMs with the exception that they could be erased. The problem was, if you wanted to erase something, you had to erase everything. This classic style of flash-memory chip is generally referred to as bulk erase. Since then, there have been quite a few innovations tailored for various applications. Apparently, the maze of choices has expanded so much that some flash-memory vendors have created some very nice utilities for helping with the decision process. One such "product selector" utility is Intel's flash-memory Solutions Wizard. Whether your application is simply an EPROM replacement in a small embedded system or you want a complete solution, it is probably just a few mouse clicks away.

Now, vendors are supplanting bulk-erase flash-memory parts with sector-erase parts which divide the flash-memory memory space into several sectors or blocks. The sector-erase parts fall into two basic categories, symmetric and asymmetric. Symmetric block parts contain a uniform sector size, commonly 64 KB, which makes them well suited to pure data storage or disk-drive replacement applications. Asymmetric or boot block parts usually contain a few sectors of varying sizes such as 8-KB and 16-KB in addition to several larger fixed size blocks. Asymmetric parts are frequently used in code-storage applications where some of the small sectors may be used for storing a bootloader.

The flash-memory vendors have also found a solution to another one of the bulk-erase generation weaknesses. In the past, as long as a flash-memory part was being written to, it could not be read. The latest parts incorporate a feature called dual bank or dual page mode which allows one bank to be written to while the other can be read from. This is a useful feature in many applications including both code and data storage.

Chip Vendors

AMD offers a full line of flash-memory parts suitable for developing just about any application you can imagine, covering 1.8-V, 3-V, and 5-V supplies. AMD has you covered with just about any packaging needs you might have too, from DIP to FBGA and Known Good Die form. For more info, including databook, datasheets and applications notes, take a look at AMD's technical literature.

AMD also has driver software for 5-V and 3-V flash-memory memory devices and Common flash-memory Interface (CFI) driver software for devices that support the CFI standard.

Atmel offers standard parallel-access flash-memory parts as well as serial access flash-memory parts with small sector sizes making them well suited for data storage applications such as voice recording. You'll find more info in Atmel's online datasheets and application notes.

Fujitsu offers a range of flash-memory parts as well as some multi-chip parts that integerage flash-memory and SRAM in a single package (nice when you are low on board space!).

Hyundai offers a very nice overview including a glossary of common terms. Check out Hyundai's selection guide for a list of available parts and their datasheets.

Intel offers a few different product selection aids to help you navigate the many possibilities they offer. The flash-memory Memory Solutions Wizard is great for searching for a solution based on your application needs. The Product selector matrix is great for matching your embedded CPU to the optimal Intel flash-memory solution. And, the Parametric selector guide will help you select flash-memory parts based on your specifications.

Of course, you can find all of Intel's flash-memory datasheets and application notes online.

Intel jointly developed the Common flash-memory Interface specification with AMD, Sharp, and Fujitsu. CFI has since become a JEDEC standard. Intel has an excellent overview on CFI as well as documentation and excellent reference code.

Micron originally entered the flash-memory market as an Intel licensee but has since begun to innovate with products such as Syncflash-memory which makes it possible for flash-memory memory to coexist on the same bus as SDRAM. Micron offers a product selector guide, a flash-memory product guide and data sheets online.

Mitsubishi (overview) offers a range of flash-memory products including 1-, 8- and 16-MB parts as well as a selection of multichip packages combining flash-memory and SRAM.

Sharp offers from 2- to 32-MB parts in both symmetric and boot- block varieties. Sharp's datasheets and appnotes as well as a very informative FAQ are available online. Sharp also offers driver software for your application.

ST Microelectronics also offers a variety of 3-V and 5-V products, with online application notes and flash-memory driver software. And most recently, ST Microelectronics has added a 32-MB 1.8-V flash-memory part with an impressive 3-5ns access time.

Organizations

JEDEC (Joint Electron Device Engineering Council) is a semiconductor engineering standards body created by the Electronic Industries Alliance (EIA) to help with the standardization of semiconductor products.

The JEDEC website has numerous industry-standards documents accessible free of charge. I have listed a few documents here that are relevant to flash-memory memory.

Common flash-memory Interface (CFI), JEDEC Standard 68, September 1999

Common flash-memory Interface (CFI) ID Codes, JEDEC Publication No. 137, September 1999

Standard Manufacturer’s Identification Code, JEDEC Publication 106-G, March 19, 1999

If you would like to add any information on this topic or request a
specific topic to be covered, contact Benjamin Day. Ben Day works for Schweitzer Engineering Laboratories in Pullman, Washington making electric power safer, more reliable, and more economical.

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