M16C Family, M16C/Tiny Series

Compatibilities Maintained in M16C Family Reduce System Development and Production Costs; New 16-bit M16C/Tiny Series Microcomputers Are Faster, Smaller

The Renesas M16C family of 16-bit microcomputers has been developed for long-term use in a wide variety of embedded systems for consumer and industrial markets, among others. The popular family includes a large number of product series that retain compatibility over time. This article discusses that compatibility, a key feature of the M16C family, then describes developments in the M16C/Tiny series, versatile devices with low pin counts and small ROM sizes.

Semiconductors designed for new manufacturing technologies tend, in the case of many microcomputers, to undergo changes with successive generations. Typical changes include different package dimensions and pin counts, different CPU instruction sets, and different designs and sets of peripheral functions. Such changes often force design teams to modify systems that use the revised microcomputers. The engineers may have to redesign board layouts to accommodate the new devices, revise their software programs, etc. These modifications cause delays in product development cycles and impose extra engineering and manufacturing costs. Such problems can be avoided, though, if the systems use microcomputers that maintain compatibility with previous models. The same board can still be used and software changes aren't needed.

To help customers minimize system development time, engineering expense and production costs, Renesas is rigorous about retaining extensive compatibility within the M16C family of 16-bit microcomputers. We develop new models and upgrade existing ones based on the concept of having "no end of life"; (see Figure). All devices in the same series are carefully designed and managed to maintain compatibility—not just in their instruction sets (code compatibility), but also in their peripheral functions and pin layouts. As a result, system engineers have exceptional design flexibility. They can switch to another microcomputer in a series in the M16C family without having to redesign their board layout and with few if any changes to software programs. This feature is a main reason for the popularity of the M16C product line.

Besides compatibility, microcomputers in the M16C family offer many other features valuable for embedded system applications. For example, frequently used instructions are executed in a single cycle and are stored as a single byte. The compact code reduces the required on-chip ROM and can allow the use of a lower-cost microcomputer. It also reduces the number of program steps, enabling application performance to be higher than might be expected at a particular clock frequency. The number of bus accesses is reduced, too, for less current consumption and noise.

At the heart of the M16C series are the economical microcomputers in the M16C/60 series—the most widely used devices in the product line and true workhorses for embedded systems. They have a maximum clock frequency of 24MHz, provide up to 512Kbytes of on-chip flash or mask ROM, and have excellent EMI/EMS characteristics. The M16C/Tiny series microcomputers are based on those M16C/60 devices, but use smaller packages with fewer pins and offer less ROM, up to 128Kbytes. They were developed for applications in which systems must be configured at even lower cost.

One feature of M16C/Tiny devices that merits special mention is an analog-to-digital converter (A/D or ADC) that incorporates two sample-and-hold circuits, plus a circuit for using these functions with precise timing control. This functionality, combined with notable EMI/EMS performance and low cost, makes M16C/Tiny microcomputers ideal solutions for controlling three-phase AC induction motors. Not surprisingly, these devices have been widely adopted in air conditioners, refrigerators, washing machines, and other home appliances that use electric motors.

The maximum clock frequency for M16C/Tiny chips, 20MHz now, will rise to the 24MHz of M16C/60 series devices when full-scale production of new models begins this autumn. This speed enhancement will boost processing performance by 20 percent. Also this autumn, the 80-pin model will become even smaller when a 7mm x 7mm LGA package replaces the existing 12mm x 12mm QFP package. The new package uses 65-percent less circuit board space (see photograph) and makes the new M16C/Tiny devices the smallest 16-bit microcomputers Renesas offers.

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