[Original] 8-bit, 16-bit, and 32-bit MCUs compared? How to choose the right device?

Decades ago, 8-bit microcontrollers (MCUs) took the industry by storm, but now 8-bit MCUs are giving way to 32-bit architectures, and industry analysts point out that 32-bit and 8-bit MCUs are still growing. However, the earliest users of MCUs still remember BASIC and Microchip PIC, but the latest Arduino Uno is a typical example of the transition from 8-bit to 32-bit architecture. Even if your current application only requires an 8-bit architecture, due to the growing demand for so-called "smart" devices , 8 bits will not be enough in the future. Fortunately, there are now a large number of open source development tools that can be used by aggressive engineers who are eager to "take risks."

Figure 1: Register size is a key differentiator in system architecture and also affects system performance.

What do we mean when we say that a microcontroller is 8-bit or 32-bit? These numbers refer to the size or width of the processor registers. An 8-bit microcontroller register, the basic memory unit of a processor, is 8 bits wide. The registers take data from the RAM memory and store it before being manipulated by the arithmetic logic unit (ALU). Therefore, larger registers mean that we can operate on larger amounts of data in fewer clock cycles. Generally speaking, larger registers give us better computing performance, which is why the central processing units (CPUs) of laptops and smartphones use a 64-bit architecture.

So what are the advantages of switching from 8-bit to 32-bit? What are the trade-offs? It takes a good understanding of the technology and your application to ensure that you make the right design decisions.

1. More memory: 32-bit architecture means you can directly access 4Gb of memory space without having to resort to special techniques such as memory paging.

2. Processing power: The new architecture benefits primarily from faster clocks and increased computing power per clock cycle. On average, this means that more throughput can be handled through a 32-bit architecture to achieve 90 to 100 MIPS; while an 8-bit microcontroller can only achieve a maximum of about 25 to 30 MIPS.

3. Energy efficiency: 32-bit architectures often utilize new circuit structures and manufacturing processes, so they must reduce transistor leakage current at lower operating voltages. This in turn improves energy efficiency processing power. This means that if you want to design something that can run for several months on a coin battery, a 32-bit architecture chip may not be the best choice. In contrast, 8-bit systems use larger process geometries and operate at 5 V, making them suitable for applications in noisy environments.

4. Cost: 32-bit platforms are generally more expensive than 8-bit platforms in areas where functionality is similar (such as memory and peripheral components). Although a cost difference is not that large, it does exist and becomes more noticeable when the product volume is large.

5. Package size: 8-bit microcontrollers are available in very small packages; some have only 6 pins. But the tiny package does not allow external devices to have many I/Os to process.

6. Ease of development: This is where you need to understand your application. Manufacturers tend to add new and more advanced features to their 32-bit architectures first. Advanced onboard devices, advanced I/O capabilities, and increased memory on 32-bit systems can be very convenient if the application requires them, although they come at the expense of coding simplicity. More advanced features can result in different clock speeds, more configuration registers that need to be adjusted to set up, and so on. In contrast, 8-bit systems tend to be relatively simple and easy to code. If your application does not require advanced features, you can actually stick with an 8-bit architecture. Both 8-bit and 32-bit architectures tend to utilize C language compilers, although many developers prefer to use assembly language on 8-bit platforms.

As the popularity of open source hardware (OSHW) has grown over the past decade, many platform developers have chosen 8-bit architectures based on cost and the fact that DIP packages (which many popular 8-bit microcontrollers use) have become more user-friendly. (Many 32-bit architectures are non-DIP packages such as surface mount packages (SMD), which are meant to be applied to machines. Hand soldering on PCBs is very difficult, and certainly not suitable for breadboards such as PDIP. Ball grid array (BGA) packages are indeed not suitable for soldering. Alas, these small packages make hand soldering of old-fashioned prototypes even more difficult.

However, today the focus is on moving OSHW from being just an educational platform to becoming a prototyping platform and even a consumer product platform. As a result, the computing and low-power performance of 32-bit systems are increasingly becoming the ideal "maker artifact" that wants to go from prototype to production in one go. In addition, as 32-bit-based system-on-a-chip (SoC) platforms become cheaper, integrate more practical features (such as Bluetooth Low Energy, WiFi and NFC) and become easier to use, manufacturers will undoubtedly continue to produce these low-cost open source development boards. The purpose is to simply understand the workings and be able to fine-tune each configuration register setting to maximize performance, which most manufacturers are willing to do.

32-bit hardware platforms are gaining more and more recognition, and many manufacturers offer such products, including BeagleBone, Texas Instruments, STMicroelectronics, Cypress, Arduino, etc. In order to more easily obtain these new platforms, Mouser has developed an open source hardware where you can choose the device platform that suits your needs.

Here are a few examples:

Need Android-powered system performance? Check out UDOO Neo.

Need an SD card slot to save data? Go get an Intel Edison or Galileo.

Need 64-pin digital I/O? Look for a BeagleBone Green.

Need more I/O? Try STM32 Nucleo.

Want to train STEM students in advanced development? These students are used to using the Arduino ecosystem, so the Arduino 101 board may be for you.

There are many more options