Weak current College】 【noteworthy microcontroller board design principles】.

<br> (1) in the components of the layout should be interrelated components to put close to some, for example, clock generator, crystal oscillator, CPU clock input noise is easy to produce, in place of time should bring them nearer. For .those who are easy to produce noise of devices, low-current circuit, high-current circuit-switching circuits, etc., should, as far as possible away from the microprocessor logic control circuitry and memory (ROM, RAM), if possible, .can be made of the circuit in addition to facilitate anti-interference circuit board, improve the reliability of the circuit. <br> <br> (2) as far as key components, such as ROM, RAM and other chip decoupling capacitor is installed .next. In fact, PCB wiring, wiring and connector pin and so may contain large inductive effect. Large inductance might Vcc alignment caused serious switching noise spikes. Prevent the Vcc alignment on switching noise Spike's unique approach, is in the VCC and power between the .places a 0.1uF e decoupling capacitor. If the circuit board using surface mount components, you can use the sheet capacitance directly next to a symbol, fixed in the VCC PIN. It is best to use ceramic capacitors, this is because such capacitors with low .electrostatic dissipation (ESL) and high-frequency impedance, this capacitor temperature and time media stability is also very good. Try not to use tantalum capacitor, because in the high frequency of impedance under it. <br> <br> Seated decoupling capacitor, .take note of the following: <br> Road In printed circuit boards of power input crossover 100uF of electrolytic capacitors, if volume allows, electrical capacity larger is better. <br> Road In principle each IC chip are placed next to one of the ceramic .capacitor 0.01uF, if the Board of the gap is too small and placement, the can around every 10 chips, place a 1-10 of tantalum capacitor. <br> Road For a antijamming ability weak, turn-off time current change large components .and RAM, ROM, and other storage components, should be in the power cable (Vcc) and ground between access decoupling capacitor. <br> Road Capacitor leads not too long, especially high-frequency bypass capacitor cannot lead. <br> <br .> (3) in the microcomputer control system, the ground of many kinds, systematically, shield and, logically, analog, and whether the layout is reasonable, the ground will determine PCB anti-interference ability. In the design of the ground and pick .up spot, you should consider the following issues: <br> Road Logic and analog to separate wiring, can not be combined, will their ground with appropriate power ground wire. At design time, simulation of the ground should be bold, and try to .increase the leadout area of the grounding. In General, for input and output of analog signals, and microcontroller circuit between the best isolation through optical coupling. <br> Road In the design of logic circuits for printed circuit board, its ground-loop form .should constitute, improve circuit anti-interference ability. <br> Road Ground should be as rough. If the ground is very thin, ground resistance will be larger, ground potential with current changes, causing the signal level instability, leading to the descent of .anti-interference ability. In the wiring space permitting, to ensure that the main ground of the width of at least 2 ~ 3mm above symbol pin grounded around the 1.5mm. <br> Road It is necessary to pay attention to the choice of receiving .stations. When the signal frequency is lower than on the Board, because of the wiring 1MHz and components between electromagnetic induction to low impact, and earthing circuit formation in circulating on the interference of the larger, so you want to use a little grounding, so .it does not form a loop. When the signal frequency is higher than on the Board, because of the wiring 10MHz inductance effect obvious, ground impedance becomes very large, ground circuit formation of circulation is no longer a major problem. So should adopt more grounded ., minimize ground impedance. <br> Road Power cable in addition to the layout according to the current size as far as possible, bold line width, the wiring, the power cable and the ground of alignment direction and data line alignment to the parties as .agreed at the layout of the final, with ground wire to the back of the circuit board without alignment of fill, these methods will help to strengthen the capacity of anti-interference circuit. <br> Road Data line width and wide as possible, to .reduce resistance. Data line width at least not less than 0.3mm (12mil), if you use 0.46 ~ 0.5mm (18mil ~ 20mil) is more ideal. <br> Road Due to circuit board of a through-hole will create about 10pF .of capacitive effect, high frequency circuit, will introduce too much interference, wiring, you should minimize the number of the hole. Again, too many hole also reduces the mechanical strength of the Board..