When it comes to specifying and buying microcontrollers, designers have many alternatives, and making the right choice among them is critical to the success of an embedded-system project. According to a recent CMP Media survey, code compatibility is a primary MCU selection criterion because choosing an MCU based on a code-compatible platform allows reuse of designs and tools. This reduces the system development cycle and shortens time-to-market, while also reducing the resources devoted to retraining staff. The result is lower overall cost and bill of materials (BOM), as well as enhanced flash and peripheral options.
Choosing a compatible MCU also avoids difficulties over the long term. It increases manufacturing flexibility, making it easier to react to specification changes while trying to maintain production schedules. This avoids the need for overcompensation to avoid shipment delays, which can create costly inventory excesses. The flexibility also ensures a smooth migration path to higher-performance devices.
A sure way to obtain compatibility is to select a platform MCU. Many MCU suppliers have developed and continue to expand the standard platform concept, which can be defined as a broad line of MCUs that provides a smooth migration path from 8-bit through 32-bit performance without significant additional engineering investment.
Companies that choose devices from a broad MCU platform gain access to a wide choice of flash memory and peripherals — plus the most complete pin and code compatibility — for optimizing system designs today and in the future. For example, development teams can move between MCU versions with diverse amounts of on-chip flash without changing hardware and losing their investments in code base and development tools.
The platform concept embraces code compatibility as a primary tenet. Product road maps for MCU platforms evolve in a controlled manner so that new devices can run existing programs, even while offering greater or lesser features and capabilities to meet shifting application requirements. This preserves the code base and knowledge the development engineers have built. It allows easy upward performance and downward cost migration, and makes it easy to leverage existing engineering knowledge into new system designs.
In industrial-control applications, for example, better control algorithms are continually being invented. A platform MCU enables an improved algorithm, which may require more memory and greater processing throughput to implement, to be incorporated into an enhanced control system with a minimum of design and debug effort.
A comprehensive platform MCU product line includes many flash options, including on-chip flash in memory sizes from 16 to 512 kbytes, along with various sizes of RAM. Platform MCUs offer an extensive array of I/O options, as well as many on-chip peripherals, such as timers, motor controller functions, CAN controllers, USB functions, LCD controllers and data converters, among others. Beyond that, other valuable features might be incorporated into the platform, such as pin compatibility, which enables multipurpose circuit boards, and EMI/EMS protection, which enhances system reliability in automotive, industrial-control and consumer applications.
Shorter development, less risk
OEMs that choose platform MCUs can cut weeks off design cycles compared with using incompatible devices, and reduce design risk in the process. A situation faced by a North American automotive supplier illustrates this point. Its customer, a major vehicle manufacturer, drastically shortened the development-to-production cycle time for new body control designs.
In an application where nickels and dimes count, the supplier's engineers selected whichever MCU was cheapest at the time. However, because every design was usable only once, development cycle times were too long. The solution was a standard platform MCU with the best EMI/EMS performance that covered the 8- to 16-bit price/performance range demanded by variants of the body control designs. The savings in component cost resulting from superior EMI/EMS performance more than offset the cost of not using the cheapest MCU.
In the manufacturing department of an OEM, the primary objectives are to produce in volume a high-quality product that meets total BOM cost requirements. Other typical goals are to reduce the number of operation processes, reworks, customer returns, cost of operations and inventory levels. Today, because end users and distribution chains demand that suppliers be more responsive and flexible, manufacturing managers must speed up overall production time while simultaneously becoming better at handling rapid changes in the product mix.
The need for flexibility is exemplified by a common situation that challenges white-goods manufacturers. In one situation, a major retailer had kicked off a big appliance sale, but misjudged the product mix and volume. The retailer demanded a remix of product shipments. The manufacturer, to maintain its competitive advantage, had to respond without a second thought, while possibly facing an enormous rise in excess inventory, incurring large manufacturing-changeover expenses and disrupting shipments to other customers.
Fortunately, in this case, the manufacturer's embedded control system used a platform. That critical design decision allowed the company to produce the required products for any set of customer demands simply by mixing electrically and mechanically "plug-compatible" modules built from common parts. Specifically, by choosing a standard MCU platform with common pin layouts from 20 to 144 pins, software compatibility and a price/performance range from 8 bits to 32 bits, the manufacturer designed one common printed-circuit board with standard components that could serve the cost, feature and performance requirements of multiple products.
Because the white-goods manufacturer used a highly flexible, easy-to-build platform concept focused on minimum parts count and maximum flexibility, it was also able to reduce manufacturing complexity and BOM costs by eliminating up to 60 cents' worth of capacitors, resistors and ferrite beads, thanks to the chosen MCU platform's exceptional EMI/EMS capability.
MCU optimization simplified
Experience has proved that using a platform MCU is a good way to solve common design-engineering problems related to fast-changing specifications and multiple designs for similar products. MCU optimization is greatly eased. If a product needs more features or memory, simply move up to the next-higher family member. If cost considerations force a switch to a smaller memory or feature set, just move down to the next-lower device in the MCU platform.
If the devices are both pin- and software-compatible, no software must be rewritten, nor is there any need to change the surrounding components. Quite possibly, qualification testing time and cost can be reduced or eliminated as a result. A large number of projects have proven that applying an MCU platform approach to system design can save development time and cut total system cost.
The range of products in a solid MCU platform simplifies the process of selecting a microcontroller with the best system price/performance advantage. OEMs can readily select an MCU that minimizes overall system cost, supports the design schedule, scales to meet future requirements, has the flexibility to accommodate changing market needs and supports manufacturing goals.
Richard Sessions (firstname.lastname@example.org) is director, market evangelist, at Renesas Technology America Inc. (San Jose, Calif.).