Ⅰ.Basic Rules for Selecting Electronic Components

A simple guide to electronic components.

a、Universal Rule

  We need to choose widely-used components to reduce the development risks.

b、High Cost Effective Rule

  It is necessary to select electronic components with lower price to reduce cost when they have the similar performance and utilization .  　　

c、Purchasing Rule

  The components should be easily purchased, and have a shorter supply cycle.　

d、Sustainable Development Rule

  Try to choose those that will not be discontinued for the foreseeable time.　　

e、Alternative Rule

  Try to select components that have multiple pin-to-pin compatible chip brands. 

f、Upwards-Compatible Rule

  Try to choose components often used by the previous products.　

g、Resources-saving Rule

  Maximize all the functions and pins of the components.

The chip selection should consider each dimension.

Figure 1 Electronic Components in Circuit Board

Ⅱ. Pay attention to the chip attribute in the entire process .

1. It is necessary to consider the trial and volume production conditions when selecting a model. 

  It would be better to concern the purchasing price, supply cycle and sample application of a small order, the same to a mass one. When the volume becomes larger, the supply price may has no competitive advantage, or causes the insufficient capacity. In addition, we should pick up corresponding suppliers according to the actual procurement. 

  For example, the original factory will not supply items directly, but through the agent. The supply volume of some agencies is limited and the chip is not widely-used in the industry so the price of this chip is very expensive in Taobao. A chip dealer once said that this chip price is speculated by some guys, causing the price reaching high.

2. Whether the life cycle of component matches that of the product

  Generally speaking, the selected components should have more than 5 years life cycle and complete product development layout. For instance, a new hardware platform used at the time becomes a mature platform for a board order which exceeds one million.

  Because of the long switching period, the output of the new product increased gradually after 1 ~ 2 years of development. A DSP circuit with SDRAM peripheral storage is going to have quantitative production , Micron Technology and other big memory chip manufacturers announced that they would stop producing SDRAM. The inventory-chip hoarding be caused when the product produced quantitatively, then a Taiwan factory be picked up to produce the components as second-source option. Thus selecting the right components needs a good preparation. 

3. Except the consideration of performance and laboratory environment, there is a need to consider the whole life cycle scenario.

Ⅲ. Specific model selection | processor selection

  There are many factors needed to consider when selecting a good processor. Not only the hardware interface, but the related operation systems and matching development tools and emulators, also the microprocessor experience of engineers and the situation of software support and so on.　

  The factors of embedded-microprocessor model selection: microprocessor, as a core chip , its functions, performance and reliability are highly valued in product developments. Because the more resources it has, the more powerful it is, the shorter the product development cycle and the higher the project success rate. However, any microprocessor can not be perfect to meet the needs of every user, so this involves the selection of the problem.

a. Application Area

  The function and performance of a product decides its application area. Definite application area may narrow selecting range of models.For example, the working conditions of the products in the industrial control field are usually harsh, and the working temperature of the chip is usually wide, so we have to choose the industrial grade chip rather than the civil ones. So far the more common application areas include aerospace, communications, computers, industrial control, medical systems, consumer electronics, automotive electronics and so on.

b. Self-contained Resources

  There are some problems met with people: what is the basic frequency? Is there a built-in Ethernet MAC? How many I/O ports are there? What interfaces are they carrying? Does it support online simulation? Does it support OS and what OS does it support? Does it have an external storage interface? ......All the questions above are related to what resources the chip contains itself. What kind of resource comes with microprocessor is an important factor for selection. The more the chip comes with resources close to the product's demand, the simpler the product development is.

c. Extensible Resources

  The requirements for resources are relatively high when hardware platform support OS, RAM and ROM. Chips generally have built-in RAM and ROM, but their capacity is generally very small. Built-in 512KB is very large, but generally running OS is more than megabytes. This requires chip extensible memory.

d. Power Consumption

  Low power consumption becomes a important indicator to select model for chips, because its has many advantages. Products with low power consumption can save money and energy, reduce environmental pollution and add reliability, although it is a more abstract term literally.

e.  Package

  The common microprocessor-chip packages mainly include two types: QFR and BGA. BGA package soldering is more difficult, most small companies can not solder, but the size of packaged chip is much smaller. If the product does not require strict chip size, it is best to choose QFP package when selecting.

f. Chip’s Continuity and Technology’s Inheritance

  At present, the speed of product replacement is very fast, so we should consider the upgrade of chip when selecting the model. The inheritance of a technology is better when using the same core series of chips of same manufacturer. There is a need to consider a well-known semiconductor company, then querying its related products and making a judgment.

g.  Price and Supply Guarantee

  The price and supply of chips are also the factors that must be considered. They are unstable during sampling at present. So a mass-produced chip should be selected as much as possible.

h. Emulator

  Selecting appropriate matching emulators will bring a lot of convenience to the development. The emulator is a tool for debugging hardware and low-level software. If it is not in the early stages of development, it will be difficult for product development basically. People who already have an emulator, need to consider whether it supports the selected chip during the selection process.

i. OS and Development Tools

  As a product development, software support must be considered when selecting a chip, such as what kind of OS to support. For those who have OS, it is necessary to consider whether the selected chip supports the OS during the selection process, or conversely, whether the OS supports the chip.

j. Technical Support

  The current trend is to buy services, that is, to buy technical support. A well-known semiconductor company is a better choice when selecting chips, because its technical support capability of a good company is relatively guaranteed. In addition, the maturity of the chip depends on the user’s scale and use. Selecting more widely used chips on the market will have more shared resources and bring much convenience to the development. Again, some manufacturers are good at  simple MCU applications, and some are good at industrial control or more complex applications of MCU and CPU, so they have their own advantages and disadvantages. 

  CPU according to the instruction set architecture is divided into four kinds: PowerPC, X86, MIPS, ARM. X86 executes CISC instruction set, POWERPC, MIPS and ARM follow RISC instruction set, the CPU application of RISC is mostly used for embedded systems. PowerPC in industry is mainly used in the network communication market. X86 focuses on the PC and server markets. MIPS targeted market is embedded applications such as networking, communication and digital consumption. ARM’s target market is portable and handheld computing devices, multimedia, and digital consumption products. As for the high-end processor, x86 architectures dual-core processor and MIPS architectures multi-core processor have different service orientations. The MIPS processor is easy to implement multi-core and multi-thread operations and performs well in data plane message forwarding, but the single-processor kernel structure is simple. It is obvious that MIPS is not as good as x86 and PowerPC for complex calculations and message deep processing.  Multi-core MIPS or NPs are used for data processing, and PowerPC or embedded x86 are used for control applications. The ecological environment of industry ARM is better, and there are a number of chip suppliers to provide ARM devices. In a word, A selection must take a number of comparative analysis and competitive evaluation.

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