Embedded Insight Archives
Base2 and Medical Devices
Base2 Software Design provides the expertise and experience you need on your medical device development team. While providing first-class firmware design and development for your product, we also help you solve problems in other disciplines such as electrical engineering and user interface design. Here are just some of the services that we offer:
For more information on how Base2 can help you with your medical device development, contact Michael Miu at 510/745-7773, or send an e-mail to mailto:firstname.lastname@example.org.
In the old days (not too long ago), there was only one kind of Flash memory. Today, not only do you have ICs to choose from, there are a variety of choices of removable Flash media as well. So how do you figure out what's right for your application? Let's start with the basics.
Flash is also known as EEPROM (Electrically Erasable Programmable Read-Only Memory). Just as the name implies, the EPROM can be erased with electrical signals alone. (Before Flash, the only erasable EPROMs were UV-erasable.) Flash comes in two technologies: NOR and NAND.
NOR Flash ICs are typically used in place of ROMs and PROMs. They are random-access devices where each memory location can be individually read and written (see Diagram 1). However, they are typically erased in blocks.
Diagram 1: NOR memory map for 64KB device
All CPUs that can read a ROM or EPROM can read a NOR Flash without any additional logic or special software. Also, the software required to erase and write a NOR Flash is extremely simple. All of these features make NOR Flash a good way to implement downloadable firmware as well as a multitude of other useful features.
NOR Flash has good reliability. For example, AMD now has parts that can be erased and reprogrammed 1,000,000 times. Even if you performed 10 program/erase cycles every day, you won't wear out this part for over 273 years!
NAND Flash was developed as a block access device. This means that data is read, written, and erased in blocks. More precisely, the memory is organized in blocks and pages and is accessible by pages (see Diagram 2). This type of organization is similar to hard drive or floppy disk access.
This design allows larger and larger memory footprints while keeping the same common pinout. However, the trade-off for the simpler hardware is more complex software. CPUs must use a NAND Flash device driver to access the Flash as secondary storage.
Diagram 2: NAND memory map for 8MB device
Unlike NOR Flash, NAND Flash can have bad blocks. That is, some blocks will not be usable because either the memory cannot be erased or it cannot be programmed. It is up to the software developer to decide how best to deal with bad blocks. NAND Flash comes equipped with a spare area for each page so that an ECC algorithm can be implemented.
Serial EEPROMs are worth mentioning because of their small size. Many
are available in an 8-pin SOIC (about 18 sq. mm.) Also called Non-Volatile
RAM (NVRAM), serial EEPROMs are based on NOR Flash technology where every
byte is accessible in a random fashion. They are best used for storing
parameter data such as user preferences. This is due mostly to the low
data transfer rates typical of serial EEPROMs. A couple of popular vendors
for serial EEPROMs are Microchip (http://www.microchip.com/1010/pline/memory/index.htm)
and Maxim Integrated Products
Flash is used pervasively in todays products as removable media. These products include digital cameras, MP3 players, and PDAs to name a few. There are currently several standards for removable media: SmartMedia (SSFDC), CompactFlash, MemoryStick, and MultiMediaCard (MMC) (see Diagram 3). These media typically incorporate NAND Flash technology, but some form factors such as CompactFlash and PCMCIA are also designed for hard disk and I/O applications.
Diagram 3: CompactFlash, MMC, MemoryStick, and SmartMedia (from left to right). PCMCIA not shown.
There are many considerations when choosing removable media for your product including:
Of course, the priority of these considerations will depend upon your particular industry and situation. For most applications, cost and availability of the media are the most important constraints. With this in mind, CompactFlash and SmartMedia currently give the best consumer value. These form factors are widely available in consumer electronics stores. For a 128 MB card, CompactFlash starts at around $55, and SmartMedia starts at around $47.
For more information on the removable media standards discussed here, check out the following links.
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Motorola ColdFire MCF5249
The Motorola ColdFire family is the latest generation of the venerable 68000 microprocessor. Boasting a new RISC core and machine code that is a subset of the original 68K, the ColdFire family gives a high degree of integration and a good price to performance ratio.
The latest addition to this family is the MCF5249. It incorporates the new V2 ColdFire core which dramatically decreases power consumption. At 140 MHz, the part only dissipates 183 mW (typical). Here are just a few of the features:
The MCF5249 is well-suited for portable digital audio applications with multiple audio ports, enhanced MAC controller, and high maximum clock rate. The processor is also well-suited for security and industrial applications. However, true to its 68K heritage, the processor suffers from slow multiply and divide instructions taking from 3 to 20 clock cycles to execute. DSPs and some modern microcontrollers implement a single-cycle multiply instruction which speeds up math intensive operations such digital signal processing and digital audio decoding.
The MCF5249 is currently only available in pre-production quantities
comes in both 160-pin MAPBGA and 144-pin LQFP packages. No date has been
given for final release to production. There are two part numbers you
can order right away. The XCF5249LPV120 is a 144-pin LQFP at 120 MHz.
The XCF5249VF140 is a 160-pin MAPBGA at 140 MHz. Both parts are about
$14 (Qty 100). An evaluation board is also available (P/N M5249C3). For
more information about the Motorola ColdFire MCF5249, visit the Motorola
website at http://e-www.motorola.com/webapp/sps/site/prod_summary.jsp?code=MCF5249&nodeId=03M0ylgrpxNM9.
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