Engineers often get more than they bargained for when they’re specifying microcontrollers (MCUs). Considering the thousands of MCU varieties available, it can be difficult to figure out which MCU is right for an application. MCUs range from products that cost less than 20 cents for very simple home applications to $20 32-bit MCUs that control major components of industry machinery.
The natural tendency to err on the side of greater performance or more memory may, in fact, result in needless extra cost and complexity. The lines between 8-bit, 16-bit, and 32-bit products are increasingly blurred. As a result, engineers have to ask a much broader range of questions than ever before to determine the MCU with the best performance/cost qualities for their specific application, and this trend will only continue as MCUs gain new capabilities. Before making these decisions, designers should ask themselves seven key questions.
Which architecture better fits my application, CISC or RISC?
As performance demands increase, customers tend to immediately switch from the CISC to the RISC architecture. New MCUs based on the CISC architecture run at 80 MHz to achieve 80 MIPS. For applications where there is a software legacy, or in applications such as listening to music or e-learning where music or speech must be clear and high quality, these new CISC product families provide an attractive option.
What other functions can the MCU take on?
The integration of more features into the MCU is an ongoing trend. Typical features that previously were external but not integrated include DSP functionality, power on reset (POR), and low-voltage detection (LVD). Customers should ask what other features the supplier can integrate now and plans to integrate in the future to determine if that supplier can meet the customer’s long-term needs. For example, an on-board debugging feature enables engineers to use the MCU in a target system during the development phase to access all registers internally. In addition, some customers use on-board debugging to find errors in the field.
What are each MCU’s erase/rewrite rates?
Customers have commented that sometimes there are disadvantages to having more memory on an MCU. Since the MCU typically requires programming two or three times during production, erase/rewrite speed becomes important. Newer classes of MCUs with up to 512 kbytes of flash memory can be erased and rewritten in as little as two to three seconds, compared to other MCUs that can require as much as 40 seconds.
Do core and flash performance match up?
With many MCUs, flash memory is slower than core memory, which results in the MCU copying flash memory into RAM and then executing from RAM to keep up. Engineers should look for MCUs where core performance and flash performance are matched.