Just like the 4-bit pre-microcontroller, the 8-bit MCU has been finding ways to stick around. Their features and speeds have been improving offering competitive reasons to work with them. Moving ahead with the 16- and 32-bit future may have meant that a manufacturer let their 8-bit options fall from their catalogue. The net result is that those who kept up with their 8-bit product line, have a competing product for 32-bit rivals.
Competing, you may wonder? While it’s true that a 32-bit microcontroller is fully capable of doing anything an 8-bit can do, can it perform with the same efficiency and cost-effectiveness? This depends…
The 8-bit advantage
The advantage that an 8-bit MCU has is that you only need to manipulate a small amount of data for a port to be configured or read. 8-bit devices are ideally suited and designed to interface with systems and devices that have simple input: switches, sensors, keyboards, small displays, and serial devices.
Adding intelligence to a simple home appliance is the proverbial sweet spot for an 8-bit device, as the end product needs to be inexpensive, easy to use, and has a slight edge, custom or purpose-built. Moving from the planning perspective and onto the more technical scope, the following aspects of an 8-bit design trump the 16- or 32-bit equivalent:
• Code density for an 8-bit device is much smaller.
• 8-bit microcontrollers have a wider operating voltage from 1,8 to 5,5 V DC, whereas even with 5 V tolerant inputs, the operating range of the 16-bit or 32-bit is restricted to below 3,3 V.
• 8-bit devices are more tolerant of noisy environments.
• 8-bit devices are usually more power efficient.
In general, the 32-bit microcontrollers are a better fit for applications that have a machine interface with calculation performance and software-centric designs, with an RTOS or multi-tasking. That is, they are more suited to your higher-performance applications.
However, if your application meets the following requirements, then an 8-bit MCU should be on your radar and could still be the best technical solution:
• Hardware-centric applications;
• Deterministic behaviour;
• Low sleep power consumption;
• Robust electrical characteristics, and a real-world interface.
This is apt for applications such as desktop coffee machines, toasters, key fobs, security tokens, security system sensors, toothbrushes, PC fan controllers, thermostats, and thousands of other applications.
The 8-bit Harvard architecture advantage
There are several advantages to using this architecture. The modified architecture uses a dual-bus arrangement, with data on the one and instructions on the other. This design executes instructions in a single cycle. The two-stage pipelining executes one cycle, while the next one is being accessed. This combination of architectural efficiency and ease of use enables designers to be more efficient and get more done using a PIC MCU.
An ongoing advantage is that you can migrate from one PIC MCU to another when requirements change. Using the commonly used peripherals and pinouts, and migrating a project from six to 100 pins and from 128 kB to 384 kB.
Conclusion
While the debate on 8-bit relevancy will be ongoing, the fight is between the popularity of the 32-bit devices vs the advantages an 8-bit device continues to offer. With the world moving ahead, and the tools for 32-bit development being either free or open-source, the 32-bit devices available are fully capable of replacing the 8-bits. However, 8-bit devices will put up a fight.
Ultimately, 8-bit devices handle hardware-centric applications better, and 32-bit devices handle the user interface, RTOS, or advanced applications with greater ease. And therein lies the answer. They don’t necessarily replace, but rather complement each other, and this is more evident in diverse applications that are complete systems. In single stand-alone applications, the 8-bit can supplant a 32-bit with the same ease that the 32-bit device supplants the 8-bit. Build a scaled system with delegated elements and the need for both 32-bit and 8-bit modules becomes apparent. 8-bit devices introduce scaled or delegated application capacity, cost-effectiveness, ease of use, and reduced programming complexity or density. The 32-bit devices are a better fit for applications that have a machine interface with high-performance requirements.
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