Overview
In the past 16 months, the most exciting thing in the education board market is the Raspberry Pi. The momentum of the Pi2 and Pi3 world has provoked a lot of learning enthusiasts, and we also found many hobbies. Many other commercial products have been derived from Pi. In fact, the company has also quietly launched another development board for industrial products. This type of board can be used to facilitate the rapid development of product development and verification, and can be directly embedded in the developed products. Is there sincerity? Below we slowly analyze each part of the product from the perspective of product definition and electrical engineering.
Overall functional analysis
Everyone knows that in the products used in the industry, cost and stability and perfect promotion are the most critical attributes of a product's success. Promotion is a market category, so it is not discussed here. We analyze the general function of this product from the block diagram.
As you can see from the above picture, there is nothing special about the SBC-EC9100. In fact, there is nothing fancy, and the design of multiple display methods has been cut off. Everything starts from the practical, and the low cost makes the products more competitive. It should be the original intention of this product positioning, and it is also in line with our engineers' serial port to fight the world. Indeed, too many products in our lives are silently embedded in the product, no complicated operating procedures, no beautiful display interface, everything is done internally one algorithm after another, one task after another...
At the same time, in addition to the CPU, the software task program can be placed in the eMMC, or the most convenient TF card, the stability is more user-friendly. And a user-centric embedded product that must be integrated with industry users, the SBC-EC9100 is no exception, in addition to the common anti-jamming CAN, USB2.0, 100M Ethernet Network port, industrial wide-ranging RS485, the most basic UART, there are also popular wireless WIFI+BT modules, and the signals connected in the board are I2S, I2C, PWM, ADC, SPI, RMII, all of which are sufficient Consider the many needs of industry-specific scenarios. In addition, the extended GPIO signal definition is compatible with the Raspberry Pi, and the module accessories customized for the Raspberry Pi can be used directly by the user.
There is a picture of the truth, first exposed:
positive
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Detailed interpretation
I believe that most of the products are technical experts, certainly familiar with the role and function of each resistor and capacitor in the circuit, so it is not important to analyze the principle of the circuit, find a few technical points to share:
processor
The processor is listed here because our design selection is inseparable from the processor. The SBC-EC9100 uses i.MX6UL, a Freescale high-performance ARM, CortexA7 core with a frequency of 528MHz. At the same time, the minimum system configuration is 512M DDR and 4GB eMMC. This performance is sufficient for general industrial control, medical equipment, experimental instruments and other embedded products. Let's take a picture of the CPU platform:
power supply
The power supply is the fundamental guarantee of a product. Without a good power supply, no strong performance can be exerted. The SBC-EC9100 power supply uses FSL's latest power management chip PF3001. The design of other places is also quite satisfactory. All the performance is the primary goal, and no component is saved without cutting corners.
Experience sharing: Although the standard circuit of SBC-EC9100 seems to be unremarkable, but it does hide a bright spot - overvoltage protection circuit, please see the following figure:
Everyone is engaged in technology, and I will not go into details here. How? Is this recommendation correct? The circuit is simple but very practical, and the cost is low. I think that the children's shoes can be used in your products, whether they are copied or used directly, without any risk of infringement and no patent fees.
Internal circuit
Throughout the circuit schematic and PCB layout of the SBC-EC9100, it can be seen that engineers have some experience in signal integrity, maximizing the performance guarantee of the entire product.
Experience sharing: The important clock signals in the entire product have anti-reflection processing, as shown below:
Power supply retraction, EMC suppression, etc...
The equal length processing of DDR in Layout, the equal length of differential, and impedance processing all reveal the engineer's understanding of the hardware design of the entire product.
Interface Circuit
For the respect of the products, in the SBC-EC9100, the engineers added complete ESD protection and EMC processing circuits to each interface circuit;
Experience sharing: It should be the limitation of product structure and the positioning of the evaluation board. In addition to the lightning protection design, RS485 circuit has perfect circuit design such as termination balance resistor and upper and lower level guarantee.
In addition, here we focus on the CAN interface circuit, we all know that the biggest advantage of the can interface is the strong anti-interference. In addition to the standard circuit, the SBC-EC9100 also provides the actual application circuit for performance guarantee, as follows:
Theoretical description of the CAN bus:
The waveforms when the termination resistors and anti-interference capacitors are removed at no load are ideal, as shown in the following figure:
After adding anti-interference capacitor, the waveform will slow down the falling edge due to RC charging and discharging. Combined with theoretical calculation: RC circuit is (the data here is from the data sheet of CAN chip): R=Rin=38.5K, C=Ccan- Cap+Cload=20pF+56pF=76pF, time constant: ζ=RC=38.5K*76pF=2.926X10-6S≈3uS, 3RC=3*3uS=9uS, 5RC=5*3uS=15uS. The actual waveform is as follows:
It can be seen that the capacitance has a certain influence on the signal. We all know that in practical applications, there will be a lot of interference signals on the network cable. At this time, the capacitors will play a unique role. Now, the contribution of the practical application of the circuit diagram is a reminder of the role of a brick-and-mortar. Engineers share their experiences. Finally, how to design in practical applications is a matter of opinion. (Thank you especially to my colleague John, thank you for measuring the waveform and data of the CAN bus for us so carefully).
summary:
From SBC-EC9100 project to finished product, every step of the work is devoted to the hard work of engineers. In the era of rapid development of electronic products, we just did one thing, that is, take a circuit to make this chip work smoothly, thank you very much NXP (freescale) provided us with this excellent processor, and thanked the company for deciding to do this project, so that we were fortunate to participate. In particular, I hope that the low-cost and high-performance features of the SBC-EC9100 will be recognized by the market and loved by everyone, becoming the darling of the market. Finally, we all know that we lack software at this time. It depends on every engineer who chooses this product. With your participation, you can become a complete product and truly reflect its value...
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