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Rumours of the death of the 8bit microcontroller have been greatly exaggerated

How Silicon Labs solves the problem of exposing the resources of a large device in a compact package

When it launched the Cortex-M range in 2004, ARM brought 32bit processing to what had, essentially, been an 8bit world. The first core – the Cortex-M3 – was adopted enthusiastically by a range of companies. ARM has since added the M0, M0+, M4 and, most recently, the M7.

The arrival of the Cortex-M family prompted many people to predict the imminent demise of the 8bit microcontroller. And yet 8bit devices continue to be designed into a range of applications. In fact, market researcher Gartner found that, in 2014, 8bit and 32bit MCUs held almost equal market shares when it came to revenue.

So, despite the attractions of the 32bit MCU – more processing power, more memory and so on – 8bit parts must have something going for them: after all, some 32bit MCU developers continue to expand their 8bit portfolios. But what is it and how long will the devices remain in favour?

According to Lucio di Jasio, strategic marketing manager with Microchip: “With the right balance between hardware and software and new tools that reduce development effort and timescales, the place for 8bit MCUs in a wide range of applications seems more assured than ever.”

Tom Pannell, MCU marketing manager with Silicon Laboratories, said: “Not every app needs a lot of I/O or high performance. Only a few apps need GHz or even hundreds of MHz. many things we interact with on a daily basis are simple; they might just turn an LED on or off or run a simple control algorithm. These apps don’t need a lot of complexity or a lot of memory and are well suited to 8bit MCUs.”

Perhaps part of the problem – if it is a problem – is that designers associate 8bit MCUs with 30 year old technology, whereas 32bit devices are seen as being closer to the ‘cutting edge’. But Microchip and Silicon Labs argue that 8bit MCUs have made significant steps forward over the years and that the 8051 based devices of the past bear no relationship to today’s parts.

Pannell explained. “We like to show designers that if they are worried about 8bit performance, we can help because 8bit MCUs are faster than ever before. Some customers are used to 8bit MCUs running at 8MHz, but we have an 8051 based device that runs at 100MHz and a 72MHz part in our EFM8 range. These MCUs have high performance analogue blocks, including a 14bit A/D converter and a D/A converter that runs at 12ksample/s.”

“We have to find out what performance they’re looking for and whether we can meet those performance needs – and a lot of times, we can. Our digital peripherals are hardware blocks and don’t need to be emulated using the MCU. But cost is often the most important requirement,” he said.

Steve Drehbol, vice president of Microchip’s 8bit MCU business, noted that, in order to be competitive, his products needed to support fast development cycles, to have highly functional peripherals and to have a good balance between hardware and software. “While 8bit devices don’t solve all of a designer’s problems,” he said, “neither do 32bit parts. There is a clear market need for 8bit MCUs, but there has to be a balance between the hardware and software elements. That’s because customer profiles are changing; nowadays, there are a lot of software engineers on a team and maybe only one person doing hardware.”

Both companies point to the burgeoning community of makers. Di Jasio said he was seeing more entrepreneurs looking at 8bit parts. “While we’ve always seen that type of customer, there are now more of them looking to get into the market.”

Fig 1: Microchip's MCC allows peripherals to be configured graphically

Pannell said he sees makers starting at a high level, using something like a Raspberry Pi. “But, eventually, they will have to go to production with a reliable piece of silicon. They may have a simple idea, but they won’t be able to use Linux, like they did on the Pi. At that point, depending on the product, they may well go to an 8bit MCU.”

Both companies also have productivity in mind, particularly when it comes to configuring peripherals. “Tools are a key part of our 8bit offering,” Pannell contended. “We have a modern 8bit development environment in Simplicity Studio and this has a configuration tool to not only handle peripherals, but also their pin outs.”

Here, Pannell is referring to the crossbar feature in some of Silicon Labs’ 8bit parts. “It provides flexibility in how to use the available I/O and where to put analogue blocks. The feature also helps to optimise board design.”

Drehbol pointed out that Microchip has developed core independent peripherals and intelligent analogue block for its 8bit parts. “These peripherals can operate without interfacing to the core. This allows more time independent and flexible peripherals to be integrated. This, in turn, has allowed us to change our approach; we can deploy empowered peripherals.”

Creating an MCU with such peripherals can be a challenge, something which Microchip is looking to handle with its MPLAB Code Configurator (MCC) tool. “Making peripherals more intelligent might look simple from the outside, but it becomes more complex inside. We have to take that burden away from the user,” Drehbol pointed out, “and we do this using graphical configuration. They don’t have to read the datasheet to find out how to hook up particular peripherals: the tool takes care of that and can reduce what could be months of development to a matter of weeks. In fact, it brings a balance between hardware and software.”

According to Drehbol, MCC has been available for about a year and Microchip has seen around 25,000 downloads of the tool per quarter. “People are now using it as a primary tool,” he claimed, “and we’ll be developing it from configuration of peripherals by adding libraries.” Microchip is planning to launch the latest update to MCC shortly and it’s likely this will include libraries for such features as TCP/IP, LIN and touch interfaces.

While 32bit MCUs have the attention of many designers, 8bit parts remain viable design choices. Pannell concluded: “For designers who have to watch every penny and for whom being able to squeeze and optimise a design matters, if they can get it done with an 8bit MCU, they will prefer that because of cost.”

In di Jasio’s opinion: “With the right balance between hardware and software, and new tools that dramatically reduce development effort and timescales, the place for 8bit microcontrollers in a wide range of applications seems more assured than ever.”

Josh Norem, an MCU applications engineer with Silicon Labs, says that asking whether a 32bit part or an 8bit part is better is not a logical question. “A much better question,” he contends, “is ‘which MCU will best help me solve the problem I’m working on?’.” And, for a wide range of applications – including those being targeted at the IoT – the answer could well be an 8bit part.

Author
Graham Pitcher

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