(1) as far as possible in key components such as ROM, RAM and other chip decoupling capacitors next to install. In fact, the printed circuit board traces, pin connection and wiring and so may contain a large inductance. Large inductance may cause serious Vcc go online switching noise spikes. Prevent switching noise spikes Vcc go online the only way is to be placed between the VCC and the power supply to a 0.1uF decoupling capacitor electronics. If the circuit board using surface mount components, chip capacitors can be directly adjacent to the elements, the Vcc pin fixation. It is best to use porcelain capacitors, this is because the capacitor has a low static losses (ESL) and high frequency impedance, while the temperature and time of this capacitance stability is very good media. Try not to use tantalum capacitors, because the impedance at high frequencies it is higher.

Decoupling capacitor in place when the need to pay attention to the following:
• The printed circuit board power input jumper around 100uF electrolytic capacitor, if the volume permitting, some of the better large capacitor.
* In principle, each IC chip needs to be placed next to the tiles of a 0.01uF capacitor, if the board is too small to be placed no less than the gap, you can chip about every 10 to place a 1 to 10 of tantalum capacitors.
• For anti-jamming, low shutdown current of change in major components and RAM, ROM and other storage devices, power lines should be (Vcc) and ground access between the decoupling capacitor.
The lead of capacitor should not be too long, especially not with high-frequency bypass capacitor leads.

(2) components of the layout, the components should be as much as possible about each other too close to the release of some, for example, clock generator, crystal oscillator, CPU clock inputs are easy to produce noise when in place should be close to some of them . For easy to produce noise devices, low current circuit, high current circuit switching circuit, as far as possible away from the logic control circuit microcontroller and memory circuits (ROM, RAM), if possible, they can be made of other circuit circuit board, it is a good anti-jamming, to improve circuit reliability.

(3) in the SCM system, there are many types of ground, a systematic, shielding, the logic, the simulation in such ground if the layout is reasonable, will determine the board's anti-jamming capability.
Ground wire and ground point in the design, it should consider the following questions:
* Logical and analog ground to separate the wiring, can not be combined, to their respective ground were connected with the corresponding power ground. In the design, simulation ground should be bold, and try to increase the terminal's ground area. In general, the input and output of the analog signal, and the best among the MCU circuit isolation via optocouplers.
• The design of printed circuit boards, logic circuits, its ground shall constitute a closed loop form, to improve anti-interference ability of the circuit.
* Should be the rough ground. If the ground is very thin, then the ground resistance will be greater, resulting in ground potential varies with the current, resulting in signal level instability, resulting in decreased anti-interference circuit. In the routing space permitting, to ensure that the width of the main ground at least 2 ~ 3mm above the ground line component pin should be about 1.5mm.
* Pay attention to the choice of access sites. When the circuit board signal frequency less than 1MHz, because of wiring and components have little effect between the electromagnetic induction, and grounding circuit formed by the interference of large circulation, so using a little ground, so that it does not form a loop. When the circuit board signal frequency higher than 10MHz, due to wiring inductance effects were significant, ground impedance becomes large, then the formation of the circulation circuit ground is no longer a major problem. Therefore, multi-point grounding should be used, to minimize ground impedance.
• Since the board consists of a hole will bring about 10pF capacitance effect, which for the high-frequency circuits, it would introduce too much interference, so the wiring, they should minimize the number of vias. Again, too much can also cause the circuit board through-hole mechanical strength decrease.
* The width of the data line width should be possible to reduce the impedance. The width of the data line at least not less than 0.3mm (12mil), if using 0.46 ~ 0.5mm (18mil ~ 20mil) will be desirable.
* Layout of the power cord in addition to the size of as much as possible under the current alignment of the width of bold things, the wiring should also make the power line, ground wire alignment direction of the alignment with the data line side body line work in the wiring end, land Line the bottom of the circuit board where there is no alignment covered, these methods will help to enhance the circuit's noise immunity.