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8bit microcontrollers: Still going

Posted: 01 Apr 2005 ?? ?Print Version ?Bookmark and Share

Keywords:embedded systems? mcu? microprocessor? dsp? 8bit?

Although high-end processors, especially 32bit MCUs, tend to be the center of attention these days, 8bit MCUs are more than holding their own. In 2004, 8bit MCUs were expected to continue to lead all MCUs in revenue and unit shipments, accounting for almost 40 percent of the market's revenue, according to IC Insights. The combination of de facto standard architectures (such as the 8051 and 6811) and synthesizable, configurable implementations that are available as licensable silicon intellectual property has enabled 8bit CPUs to live on far beyond their initially dreamed-of lifetime.

The 8bit MCU continues to be the workhorse of the automotive industry. It is valued because of its cost-effective control functions, which enable consumers to enjoy the benefits of smart products in the automobile sector. For example, the BMW 745i luxury sedan contains more than sixty 8bit MCUs.

If 8bit processors were still stuck in the semiconductor process technologies in which they were originally designed in the 1980s (running at something like 2MHz), they would have quickly run out of steam. But the introduction of synthesizable MCUs, specifically designed for reuse with synchronous, flip-flop-based styles and simple clocking, has enabled portability to take advantage of the latest process technologies. As "soft" cores, these processors are also configurable, allowing the designer to optimize the MCU to the target application. Enhanced architectures combined with process portability have improved 8bit MCUs from 100,000 instructions per second in the 1980s to more than 100MIPS todaya thousandfold increase.

Clean, synthesizable cores can also take advantage of the latest EDA tool optimizations, which offer 50 percent power reduction; insertion of structures for manufacturing test; and help to automatically ensure signal integrity, manufacturability, reliability and high yield. It is absolutely preferable for designers to use proven IP for a mature architecture rather than try to invent such functionality on their own for the same purpose. This is especially important when designers are struggling to achieve the required productivity and cost-effective design to build modern SoCs. The International Technology Roadmap for Semiconductors predicts that by 2008, 95 percent of the productivity gain will be through the use of predesigned, preverified, reusable IP blocks.

Designers continue to turn to 8bit processors because of the architectures' familiarity and stability, as well as the massive design ecosystem that has been built around them. Synthesizable cores that adhere to these standard architectures enable the support of legacy software with little or no modification. That is especially important if, say, the original designer retired 10 years ago.

So, where are these 8bit MCUs going? For some applications, an 8-bitter is "just enough," providing the necessary processing "oomph" to handle the entire application's processing. This is especially true for applications that do not require a lot of processing power such as VCRs, remote controls, animated toys, toasters, refrigerators and washing machines. For many of those applications, designers can turn to highly cost-effective 0.35m and even 0.5m fabs.

Companies with high-volume designs currently implemented with a discrete 8bit MCU and other logic ICs can dramatically reduce their manufacturing costs, increase reliability and reduce power consumption by merging the entire design into a single SoC. This includes, of course, embedding the 8bit MCU and associated memories. To support this kind of move, the MCU must be 100 percent compatible with the discrete part. Costs are reduced through PCB reduction, parts reduction and taking advantage of dense modern IC process technology. As a reference, an embedded 8051 implementation can be done in approximately 12,000 gates with a silicon cost that is a fraction of a cent.

In applications requiring a 32bit processor for real data crunching, 8bit MCUs can be used to offload the comparatively larger and more power-hungry main processor. This allows the 32bit main processor to be run less often and/or at lower frequency because, while the CPU is in idle or sleep state, housekeeping functions can be managed by the 8bit MCU. In some cases, the 8bit MCU may do enough processing to allow the selection of a smaller or less-powerful 32bit processor. In real-time applications, the overall reliability of a system can be increased through the use of multiple MCUs such as an 8bit device coupled with a 16-, 32- or 64-bitter for intermittent, time-critical, low-processing tasks.

While the 32bit MCU market will undoubtedly overtake the 8bit MCU in the near future, the end is distant for venerable 8bit MCUs. They have reinvented themselves as synthesizable cores, and designers continue to find creative ways to use them in new applications. Key to their continued survival is designers' ability to quickly embed the 8bit MCUs in their latest designs.

- Meghan Le

Product Marketing Manager

Synopsys Inc.

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