| If you select a Micro, strong to noises, you get one half success |
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5th., March.,2025 |
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* No Reset pin at the IC package * No Clock input at the IC package and use internal 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 input. 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-up timeand/or hold time in many of internal flip-flops, composed registers and bufferes. Due to this violation,the dataonchip 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 phase-comparator.Anothe phase comparator input is made from a self oscillator. This means, the system clock, made from theself-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, EEPROM, 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 effect to the timing critical signals, it distrurb the bus operation and then the system shall be out ofnormal operation. Furthermore, if a noise shall be at the data bus, the active memory contents shall be modified.
According to this change, the CPU should read wrong or broken instruction word or modified and brokendata. Then,the Microshall 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 a motor-driveapplications. 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 timer shallbe reset while the motor running, the motor shall be stopped suddenly. This motor sudden stop shall cause many problems, mechanical broken, hazard at the road, power supplydamage by the kich-bak power from the motor and so on. Another is the kick-back surge from the motor. depending on the mechanical road and motor type itself,thekick-back signal is vary. As same as sudden motor stop, the sudden road change shall effect to motor-driver and depending on acase, it cause the large kick-back surge noise. The output signal from Motor-drive timer in the Micro, shall be effected by the surge noise and the noise shallbe skip the timer circuit and influences to other Micro 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 wiring is a type of noise antenna, include the sensor itself, these wires shall be effect by manyexternal electronic activities, a lader RF wave, side effect of thunders, ESD (Electronic Statics Discharge), andso on. Once a noise shall be reached to the input pin of Micro, the noise shall make a couple of of things as below; Change I/O setting. If the pin setting is ADC, it shall be back to default GPIO by the noise. As this result, the input function stop, then, the software or driver cannot finish this part of software. By this, a Micro shall wait to the finish 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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