| If you select a Micro, strong to noises, you get one half success |
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5th., Dec.,2023 |
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* No Reset pin at the package * No Clock input and use PLL.for clock. * No external CPU bus. * No direct connection to a Motor Drivers. * No direct input from sensors. Then, you can expect, your system can work stable. |
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* Reset pin At a Micro, the RESET input is noise sensitive one. Even if there is a filter at the RESET input, high
voltage, short pulse noise can skip the filter and make the CPU reset or un-known state. Now, due to the silicon technology advances, the system reset can be made on chip. this internal reset is far better than the external RESET signal in term of the noise issue. Thus you should select your Micro no RESET pin. |
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* Clock input and PLL. If a noise effect to the clock input, even if it is divided several stages, there should be the violation at set-uptimeand/or hold time in many of internal flip-flops, composed registers and bufferes. Due to this violation,thedataon chip are correupted and fall un-know sttate in. If the system clock has been supplied from PLL, the input clock is used to a referece of a phasecomparator.Anothe phase comparator input is made from a self oscillator. This means, the system clock,made fromtheself oscillator is no direct replation to the clock input.
Thus, a Micro equipped a PLL for its system clock is very strong to external noises. |
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* External Bus External bus is convenient to expand CPU system using FlashROM, SDRAMs, Video Memory, special I/Odevices and so on.
The other side, the external bus is the gtood antenna for noises and interferes. There are two(2) reasons with this;
One is the wire traces which are easy to catch noises since these are surface of the PCB. Another reason is that there are many timing critical signals at the external bus. Once a noise effecttothesecritical signals, it distrurb the bus operation and then the system shall be out of normal operation. Furthermore, if a noise shall be at the data bus, the active memory contents shall be modified. Accordingtothischange, the CPU should read wrong or broken instruction word or modified and broken data. Then,theMicroshall be execute strange operation while and shall fall malfunction in. |
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* Motor Drive Many Micro are equipped many timers and several kinds of times can be programmed for amotordrivepurpose. There are two issues with the motor drive settings. One is the sudden reset condition by the watch-dog timer or manual reset button. If the motor drive timershallbereset while the motor running, the motor shall be stopped suddenly. This motor sudden stop shallcausemanyproblems, mechanical broken, hazard at the road, power supply damage by the kich-bakpower fromthe motorand so on. Another is the kick-back surge from the motor. depending on the mechanical road and motor type itself,the kick-back signal is vary. As same as sudden motor stop, the sudden road change shall effect to motordriveanddepending on a case, it cause the large kick-back surge noise. The output signal from Motordrive timer intheMicro, shall be effected by the surge noise and the noise shall be skip the timer circuitand influences tootherMicro functions, and make the Micro operation malfunction. |
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* Sensor inputs There are many kinds of sensors and the sensors are located somewhat far from Micro. This long wiringisatype of noise antenna. Include the sensor itself, these wires shall be effect by many externalelectronicactivities,a lader RF wave, side effect of thunders, ESD (Electronic Statics Discharge), and so on. Once a noise shall be reached to the input pin of Micro, the noise shall make a couple of of things asbelow; # Change I/O setting. If the pin setting is ADC, it shall be normal GPIO by the noise. As this result,theinputfunction stop, then, the software or driver cannot finish this part of software. By this, a Micro shall waittothefinish of this I/O function complete forever. From outside, this shall be seemed to be a malfunction. "If the noise is high voltage, several KV, it shall jump over the I/O area and sperds to other areas. Then,itshallmakes the Micro some kind of malfunction. |
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* Extra There is no fixed behavior of noises. This means, we cannot predict what shall be made by noises. |
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