Author: Jacob Beningo
Choosing the right microprocessor for a particular product is a daunting task. Not only must consider many technical factors, but also consider business issues that may affect the success or failure of the project, such as the cost and delivery time.
When the project first started, people often couldn’t suppress their desire to get started immediately and prepare microcontrollers before system details were introduced. This is certainly not a good idea.
When making any decision on the microcontroller, hardware and software engineers should first design the system's high-level structure, block diagrams, and flow diagrams. Only then will sufficient information be available to begin making reasonable decisions about microcontroller selection. Here are 10 simple steps to follow to ensure that you make the right choice.
Step 1: Make a list of required hardware interfaces
Use a rough hardware block diagram to create a list of all external interfaces that the microcontroller needs to support. There are two common interface types that need to be listed. The first is the communication interface.
The system will generally use USB, I2C, SPI, UART and other peripherals. If the application requires USB or some form of Ethernet, a special note needs to be made. These interfaces have a great influence on how much program space the microcontroller needs to support.
The second interface is digital input and output, analog to digital input, PWM, and so on. Both types of interface will determine the number of pins that the microcontroller needs to provide. Figure 1 shows a common block diagram example and lists the requirements for I/O.
Figure 1: List of hardware features
Step 2: Check the software architecture
The software architecture and requirements will significantly affect the microcontroller's choice. The processing burden is light or heavy and it will be decided whether to use 80MHz DSP or 8MHz 8051. Just like hardware, it is very important to record all requirements.
For example, is there an algorithm that requires floating-point arithmetic? Is there a high frequency control loop or sensor? And estimate the time and frequency each task needs to run. Then calculate how many orders of magnitude processing capacity is needed. The size of the computing power is one of the most critical requirements for determining the microcontroller architecture and frequency.
Step 3: Select the architecture
Using the information from step 1 and step 2, an engineer should be able to begin to determine the required architectural ideas. Can an 8-bit architecture support this application? Need a 16-bit architecture? Or require 32-bit ARM core? Frequent scrutiny of these issues between the application and the required software algorithms will ultimately lead to a solution.
Don't forget there are possible future requirements and feature extensions. Just because current 8-bit microcontrollers are capable of current applications does not mean that you should not consider 16-bit microcontrollers for future expansion of functionality and ease of use.
Remember, microcontroller selection is an iterative process. You may have selected a 16-bit device in this step, but it will be better to find 32-bit ARM devices in later steps. This step only gives the engineer a correct direction.
Step 4: Determine Memory Requirements
Flash and RAM are two very critical components of any microcontroller. Make sure that the sufficiency of program space or variable space has the highest priority. Choosing a flash memory and RAM much larger than enough capacity is usually easy to do.
Don't wait until the end of the design before you realize that you need 110% of the space or some features need to be cut. This is not a joke. In fact, you can choose a device with a larger space at the beginning, and then move to a smaller device in the same chip system.
With the software architecture and the communications peripherals included in the application, engineers can estimate how much flash and RAM space the application requires. Don't forget to reserve enough space for extensions and new releases! This will solve many headache problems that may be encountered in the future.
Step 5: Start Looking for a Microcontroller
Now that you have a better idea of ​​what the microcontroller needs, you can start looking for the right microcontroller! Microcontroller vendors like Arrow, Avnet, Future Electronics are a good place to start looking for microcontrollers.
Discuss your applications and requirements with field application engineers from these vendors. Usually they will recommend a new device that is technologically advanced and can meet the requirements. However, keep in mind that they may have the urge to sell a series of microcontrollers!
The second best place is the chip vendor you are already familiar with. For example, if you have used Microchip devices in the past and have a wealth of experience, start their website.
Most chip vendors have a search engine that allows you to enter your peripheral combinations, I/O, and power requirements. The search engine will gradually narrow down the device and eventually find a device list that matches the requirements. The engineer can then carefully select the most suitable microcontroller in this list.
Step 6: Check price and power constraints
By this time, the selection process should yield many potential candidate devices. At this time, they should carefully check their power consumption requirements and prices. If the device needs to be powered from batteries and mobile devices, ensuring low device power consumption is definitely a priority.
If you can't meet the power requirements, drill down the list one by one until you pick the right ones. Don't forget to check the unit price of the processor. Although many devices will approach $1 in high-volume purchases, if it is an extremely dedicated or high-end processor, the price may be important. Don't forget this key element.
Step 7: Check Device AvailabilityAt this point you have a list of potential devices on hand, and then you need to start checking how useful each device is. Some important things to keep in mind, such as the delivery date of the device? Is there a stock at multiple distributors or takes 6 to 12 weeks for delivery? What are your requirements for usability? You don't want to get a big order but you have to wait 3 months to get it.
The next question is how new the device is and whether it can meet your product life cycle needs. If your product life cycle is 10 years, then you need to find a device that the manufacturer promises is still in production after 10 years.
Step 8: Select Development Kit
An important step in choosing a new microcontroller is to find a supporting development kit and learn the inner workings of the controller. Once engineers are keen on a device, they should look for what development kits are available.
If you can't find a useful development kit, then this device is probably not a good choice, engineers should return to find a better device. Most current development kits are less than $100. Paying more than this price (unless the kit can accommodate multiple processor modules) is a bit embarrassing. Another device may be a better choice.
Step 9: Survey Compilers and Tools
The choice of development kit basically limits the choice of microcontrollers that die. The last factor to consider is checking available compilers and tools. Most microcontrollers have many options for compilers, routine code, and debugging tools.
It is important to ensure that all necessary tools are available for this device. Without a handy tool, the development process will become extremely difficult and costly.
Step 10: Start the test
Even if the microcontroller is selected, things are not fixed. It usually takes a development kit much earlier than the first hardware prototype was created. To make full use of development kits to build test circuits and connect them to the microcontroller.
Select high-risk devices and try to get them working with the development kit. Then you may find that there are unforeseen problems with devices that you think work well, and then you are forced to choose another microcontroller.
In any case, early trials will ensure that you make the right choice, and if it is necessary to make a change, the impact will be minimized!
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