Some systems get no respect because they're not glamorous and only need an 8-bit microcontroller to fit the bill. Take a closer look, though. More 8-bit solutions are shipped than any other type of processor, and this market continues to grow.
The popularity of 8-bit microcontrollers is due to a variety of factors, with low price and low power requirements topping the list. Peripheral support is key too. Choose an analog or digital interface, and some 8-bit device probably has it. Most 32-bit processors are either standalone products or are found in custom system-on-a-chip (SoC) designs. Off-the-shelf products are usually relegated to 8- and 16-bit devices.
Often the choice of an 8-bit solution boils down to future use. A 16- or 32-bit solution typically offers an upgrade path that's superior in performance and capacity, but for a higher initial cost. It is possible to choose an 8-bit system that has more power and resources than a basic solution will require. For example, most 8-bit systems employ flash memory, allowing program upgrades in the field. Flash memory capacities for 8-bit systems have been growing, enabling significant upgrades in the future.
It can be tough for an 8-bit microcontroller going head-to-head against a 32-bit solution. Yet while using multiple 32-bit processors in a design is frequently cost-prohibitive, the use of multiple 8-bit processors is becoming more common. It also is a way for 8-bit processors to gain a significant edge over their more powerful counterparts.
The More The Merrier: Employing multiple 8-bit processors in a system makes a lot of sense from various standpoints. Renee Mitchel, America OEM's business development manager, indicates that distributed 8-bit micro-architectures can be cost-effective from a warranty standpoint. Replacing a module or board with an 8-bit processor can be very inexpensive versus replacing an entire system.
Multiple 8-bit processors have an advantage in designs with a large number of sensor points or specialized sensors. A 32-bit processor may be limited in terms of built-in I/O ports, or else require external devices to support additional I/O ports. But adding another 8-bit microcontroller increases the number of ports and boosts processing power. Because the 8-bit processors run slower than their larger counterparts, they can consume less power to provide the same functionality.
Distributed sensors is another area where 8-bit processors have an edge. The automotive industry is an excellent example of this type of design. Microcontrollers are employed all over the vehicle, from door sensors to door locks and window motor control. A centralized 32-bit processor could be used in place of this array of smaller microcontrollers, but the price would actually be higher, and the reliability would probably be lower.
Response time is frequently an issue in a distributed environment. Though perhaps slower than a 32-bit processor, an 8-bit processor may be as responsive because it doesn't have to handle the wide range of applications and services found in a single-processor environment.
The amount of interprocessor communication often dictates whether or not a system can be composed of 8-bit processors exclusively. The 8-bit processors work best when a limited amount of information must be exchanged among processors. Even where communication needs are high, the use of 8-bit processors in the design can let 16-bit or low-end 32-bit processors coordinate the system.
Another advantage of a distributed architecture is that the processors tend to be isolated along well-defined boundaries. Also, unlike 32-bit symmetrical multiprocessor (SMP) architectures, an 8-bit multiprocessor system is typically composed of different components selected to meet the needs of the system design.
For example, one processor may have a range of analog peripherals, while another might be dedicated to digital controls. Although most companies stick with a single-processor architecture, it's possible to use different processor architectures within a system, and there are many to pick from.