Historically, microcontrollers were designed as general-purpose integrated circuits with a relatively standard set of purely digital peripherals such as serial ports and timers. The microcontroller interfaced to several external analog and digital components to implement a targeted application. More recently, the trend has been one of ever-increasing levels of integration, including functional blocks for limited digital signal processing and analog circuitry. Although a case can be made for integration for the sake of integration, in reality, successful designs have complex economic tradeoffs and time-to-market considerations. Defining the correct system-level boundaries is as important as continuing with increasingly higher levels of integration.
For instance, how much of the solution should be "hard-wired" in silicon and what should be implemented by exploiting the flexibility of embedded software? How much memory should be embedded on the microcontroller versus the use of external commodity memory? Do the real-world signal levels impose reliability concerns on the highly scaled, low-voltage digital wafer fabrication geometries needed to make the large transistor counts economical?
For today's applications, system designers would achieve better cost effectiveness and functionality if they had available microcontroller solutions that properly defined these boundaries. In fact, high-quality product definition has become the most critical skill in the creation of application-specific microcontrollers.
In the days of general-purpose microcontrollers, when product definition was relegated to simply designing a faster and lower-cost version of the original product, the task focused on improved processor architecture, digital circuit design, and digital process technology. Defining application-specific microcontrollers for the next generation, however, requires expertise in targeted end equipment (product definition), analog IC design, and process technologies that can support the integration of precision analog, high-speed digital logic, and embedded flash memory. The first and, arguably, most important decision made by end equipment designers is the selection of an IC company that has proven expertise in all of these areas.
The collaboration between equipment designer and semiconductor manufacturer must start early in the design process with software simulation and hardware emulation support. This allows progression of the end equipment project in parallel with semiconductor chip development. The pre-silicon hardware/software development approach can also point out low-level problems missed in the initial product definition process, allowing for errors to be corrected prior to tape-out and reducing unplanned revisions and time-to-market.
Another key consideration for the equipment designer is the selection of a processor core that meets the application's performance and power requirements. Today, many products require application-specific, mixed-signal microcontrollers with low levels of digital noise, which allows the clean integration of high-precision analog circuitry. Also, when used in power-sensitive applications, these microcontrollers must operate with reduced active-mode current consumption while providing exceptional CPU performance.
Microcontrollers today can execute as fast as one instruction for every clock cycle, producing 1-MIPS/MHz performance. This permits developers to operate them at lower clock frequencies, and therefore at lower power dissipation, without sacrificing the performance of a given application.
The range and role of microcontrollers are changing and expanding as their capabilities advance. Therefore, the role of the semiconductor manufacturer is evolving from one of a supplier of an individual component to a "system" supplier, providing highly targeted and integrated products. Ultimately, the successful companies will be those that have end-to-end expertise: from product conception and definition to advanced process technologies that enable the low-cost manufacturing of complex mixed-signal integrated circuits.
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