Embedded Insight Archives


Embedded Insight

The Monthly Newsletter for Embedded Systems Professionals

Published by Base2 Software Design, Inc.
http://www.base2software.com mailto:info@base2software.com
February, 2002


* Base2 Services
* Embedded Systems Conference San Francisco 2002
* Dallas DS87C550 8-bit Microcontroller
* Choosing a Microcontroller



Base2 Software Design provides embedded software development services for companies doing product development. Our services include:

    * software design and development
    * hardware support services
        * board bring-up
        * engineering test
        * FCC test support
        * hardware debug
    * manufacturing support
    * formal documentation services (esp. medical devices)
    * design reviews

Our services blend especially well with product development firms where we work with a product development team to create manufacturable products. For more information on how Base2 can help you with your embedded software development needs, please call Michael Miu at 510/745-7773 or send e-mail at mailto:mmiu@base2software.com.



The Embedded Systems Conference is coming to San Francisco on March 12-16. This is the second year it will be at the Moscone Center, a change of venue from the Santa Clara Convention Center in San Jose. This tradeshow is an embedded developer's dream where you can see the latest microcontrollers, design tools, compilers, in-circuit emulators, and much more. For more information or to register, go to their website at http://www.esconline.com/sf/.



When Dallas Semiconductor introduced their new line of 8051-based microcontrollers nearly 10 years ago, you could count the number of models on one hand. Now they offer over 20 models including the Dallas DS87C550, a high-speed 8-bit microcontroller with ADC and PWM. Here is a quick list of features:

* 8051-based
* 4 clocks per instruction (8051 uses 12)
* Up to 33 MHz operation
* 3 16-bit timer/counters
* 8 KB EPROM (OTP and windowed packages)
* 8 10-bit ADCs
* 4 8-bit PWMs (cascadable to 2 16-bit PWMs)
* 2 UARTs
* 6 external interrupts
* 2 data pointers (DPTRs)
* power management

One of the biggest advantages of the Dallas microcontrollers is that their 8051 core only needs 4 clock cycles per instruction. The original 8051 needs 12 cycles. This translates into a 3X improvement in execution speed. Add to that a grab-bag of peripherals and power management functions, and you've got a great candidate for a battery-powered system-on-a-chip solution.

The successive approximation ADCs can perform a conversion in as fast as 16 us. The ADC inputs are multiplexed, so if you need simultaneous sample and conversion of multiple signals, you're going to want to use parallel external ADCs. Even so, with the fast conversion rate, you get a theoretical 62,500 samples per second on a single ADC channel.

Be careful with the I/O pins, though. The DS87C550 uses multifunction pins so that they may be used either for GPIO or for a peripheral. If you use the 16-bit expansion bus, all the external interrupts, PWMs, ADCs, and UARTs, you've only got about a dozen out of the 54 advertised GPIO pins left.

The DS87C550 is priced around 14US$ (Qty 1K). For more information about this chip, go to http://dbserv.maxim-ic.com/quick_view2.cfm?qv_pk=2962.



As embedded software designers, we are often asked, "Which microcontroller are you going to use?" If you look at all the companies that make microcontrollers, there seems to be an unending sea of choices. In fact, if you list all the 8-, 16-, and 32-bit microcontrollers on the IC Master website (http://www.icmaster.com), you get back 4,247 choices.

So how do you choose?

Microcontrollers can be selected using several simple criteria:

* performance and price
* availability
* tool compatibility
* special capabilities

You can use these criteria to narrow down your choices from thousands to just a few microcontrollers.

PERFORMANCE AND PRICE - Performance is most probably the most important issue when selecting a microcontroller. One of the most difficult things to do is determining how much processing power you need.

It is extremely important to design the software system before choosing the microcontroller. The embedded designer can then get a good idea of the complexity of the software and choose the micro accordingly. The last thing you need is to design yourself into a corner and then find that the product specification changed.

Performance is also proportional to price. For example, a Cirrus Logic EP7312 with ARM7 core runs at 74 MHz and costs roughly 15US$. The EP9312 with ARM9 core from the same company runs approximately 5X faster and costs around 3X more.

AVAILABILITY - Some microcontrollers are in short supply. If you envision shipping high volumes, make sure you select a micro that is readily available. Check with your distributor to make sure that the micros are produced in more than one foundry and possibly in more than one country. Some micros have second sources (e.g. Infineon C166 Family and the STMicroelectronics ST10 Family).

TOOL COMPATIBILITY - This is a very big consideration. Project schedules are met or blown based on the effectiveness of your development tools. Fortunately, most popular micros are supported by major manufacturers of hardware tools, software tools, and operating systems. If you must choose from a set of relatively unsupported micros, scrutinize the tool availability carefully. The availability of an integrated tool chain, an ICE, or other debugging tool may be the deciding factor.

SPECIAL CAPABILITIES - Here's where you can really narrow down your choices. Some common special capabilities include:

* system-on-a-chip
* built-in security features
* LCD controller
* RF communication
* ADCs or DACs
* communications (SPI, I2C, CAN, USB, Ethernet, IrDA)
* must interface to custom/specialized hardware
* fixed interrupt latency

When you get right down to it, choosing a microcontroller is not easy. Sometimes there are so many constraints to consider that it seems like the micro you're looking for doesn't exist. But if you keep these criteria in mind, hopefully your next microprocessor selection endeavor will be easier.


Base2 Software Design, Inc.
39510 Paseo Padre Parkway, Suite 270
Fremont, CA 94538-4741

Phone: 510/745-7773                    mailto:info@base2software.com
FAX: 800/883-4495 http://www.base2software.com


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Copyright 2002, Base2 Software Design, Inc. You may use the contents of Embedded Insight in whole or in part if you include this complete copyright notice and the following links: http://www.base2software.com. mailto:info@base2software.com.

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