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How the dynamics of microcontroller selection are changing

Outside of the apparent ability of an mcu manufacturer to deliver the right product at the right price, with the right development tools, technical support and so on, the selection of an mcu for a new design has generally started with the evaluation of bit size.

This exercise provided a simple starting point from which to start mining the specific features and capabilities of a device for a given application. Generally, it was a straightforward affair; it also allowed the mcu supplier to conveniently segment the market into 4bit, 8bit, 16bit, 32bit and beyond.

However, the discussion has moved away from a simple examination of the pros and cons (including price) of binary digits and application requirements; a new level of sophistication has emerged, based on the value that a mcu manufacturer can provide, the value of the mcu itself and the differentiation it can potentially offer.

A key advancement in mcu technology has underpinned this evolution; the ability to integrate high performance cores with high performance features and squeeze the result into small packages which can be sold at prices typically associated with those of the 16bit arena (or even 8bit in places). This immediately causes a blurring of the lines between bit sizes, particularly when you consider the capabilities of a modern 32bit mcu, such as the Renesas V850J series. The device, supplied in a 6 x 6mm 40pin WQFN package is, according to Gartner Dataquest, the best selling 32bit mcu in the world.

So, now we have an integrated 32bit mcu. But you then need to factor in that it's available in packages ranging from 40 to 144pins and with on chip flash ranging from 16k to 1Mbyte. Once you do that, you can start to see how bit size lines have blurred.

At a top level, you could say the V850J series offers a complete platform for embedded development. To use a real life example, this family is widely used in electricity meters; the line up allows an electricity meter manufacturer to use a single, completely upwards and downwards compatible device family as a standard platform for low end to high end meters. This approach minimises investment in software development and, of course, enables easy reuse of software and hardware IP.

So we now see a number of 32bit, 16bit and even 8bit mcus sharing the same space. How do you choose one over the other? Let's assume that a 16bit mcu would probably continue to cost a bit less than a 32bit mcu and let's save discussions about the commoditisation of 8bit mcus and the effect that has on 16 and 32bit spaces on one side. We come back to the functionality and differentiation that an mcu can provide – and this is what 32bit mcus offer above all else.

Take a next generation consumer medical product running Low Energy Bluetooth connected to a pc or mobile phone. A Java engine would reduce development complexity and a degree of encryption would also be useful. Have you tried running a software AES128 encryption engine from a 16bit mcu? It works on paper!

Then there are communication protocols. More things often work on paper here, like an Ethernet connection controlled by a 16bit mcu. This will come as standard in hardware in a family such as the V850J series, along with USB2.0 host and function channels that can run simultaneously, CAN and other serial interfaces that run into double digit channel numbers. These options enable the straightforward modularisation of communications, ideal for applications where the customer might have varying requirements.

And how about user interfaces? If an application only needs simple segment lcd output, then there are low cost 8 and 16bit options that can handle several hundred segments. But if more sophisticated and responsive interaction is required, you need to consider an operating system and associated graphics libraries. Once again, outside of the theoretical space, a 32bit mcu is the only thing that will thrive here.

Finally, let's consider power consumption. The V850J series is known for its low power consumption; in real time clock backup mode, it consumes 1µA, which enables the RTC to run from a 0.47F super capacitor for more than eight days. Except for the most power critical applications, there is a diminishing technical incentive to discount 32bit immediately.

But let's consider system power consumption. Inverter control can be achieved by dedicated hardware on 8 and 16bit mcus and, yes, they have their place in realising cost effective fans, pumps and appliances. But how about running sophisticated motor control algorithms, such as sensorless vector control, which not only make systems more energy efficient, but which also increase their performance and precision? These need the performance and on chip integration provided by a 32bit mcu, where the attractive price points and smaller packages are enabling advanced motor control techniques such as these to penetrate high volume applications.

It is probably too early to say that 8 and 16bit mcus no longer have a place and, for the time being at least, there is unlikely to be a 16pin 32bit mcu. But the emergence of the 32bit mcu as a complete platform solution, coupled with the differentiation it can provide, means designers can consider an mcu like V850J series as a 'software engine', rather than having to segment it into an 8/16/32bit space.

One final expectation, somehow complementing both the development of the software engine concept as well as the importance of the online community, is the presence of third party middleware, software and hardware tool support. It's easy to forget that mcu manufacturers are primarily experts in mcu hardware. Whilst developing software solutions – ranging from graphics based code generators to drivers and free of charge protocol stacks – remains an integral part of the mcu platform offering, real specialisation exists outside.

To conclude, we've discussed changing attitudes towards the selection of mcus with reference to how 'software engines' like the V850J series family can offer a complete platform solution and how the evolution of selection dynamics has gone hand in hand with the development of Web2.0 communities and extension of services offered by third party networks to provide differentiation.

Who knows where the industry will be in ten years time? Maybe Web3.0 will have taken over and we won't care but, in the meantime, one thing is for sure – the evolution of the microcontroller will not stop here.

Steve Norman, picture, is with Renesas Europe's technical marketing department.

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Steve Norman

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