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The anti - jamming enhancement in the single - chip microcomputer with the pull - up resistor

Article Source:Jocol Group Popularity:167 Published:2017-10-17 11:48:13 [SmallInBig]
NTC thermistor input impedance, acquisition rate and other factors designed I / O port of the external circuit. Generally determine the input impedance of an I / O port there are three cases. The fir...
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NTC thermistor input impedance, acquisition rate and other factors designed I / O port of the external circuit. Generally determine the input impedance of an I / O port there are three cases.

The first case: I / O port has a pull-up resistor, pull-up resistor is the I / O port input impedance. Most people use the 4K-20K resistor to do the pull-up, (PIC's B mouth internal pull-up resistance of about 20K).

Since the jamming signal also follows Ohm's law, the smaller the choice of the pull-up resistor in the presence of interference, the smaller the voltage generated by the interference signal on the resistor.

As the pull-up resistor is smaller and more power, so in the home design, the pull-up resistors are generally 10-20K, and in the case of strong interference pull-up resistance can even be as low as 1K. (If in the case of strong interference to abandon the B port pull function, be sure to use an external pull.)

The second: I / O port and other digital circuit output pin connected, then I / O port input impedance is the output of the digital circuit impedance, usually tens to hundreds of Europe.

Can be seen with the digital circuit to do the intermediary can reduce the impedance to the best, in many industrial control panel can see a large number of digital circuits is to ensure performance and protection MCU.

The third: I / O port in parallel with a small capacitor.

As the capacitor is DC blocking current, and the interference signal is instantaneous, and instantly extinguished, so the capacitor can filter the interference signal. But the cost is caused by the I / O port to collect the signal rate of decline, such as on the serial port and the capacitor is not desirable, because the capacitor will digital signal when the interference signal filter out.

For some special devices, such as the detection switch, Hall element, etc., is able to carry out and capacitance design, which is mainly because of its switch the amount of change is relatively slow, and can not form a very high rate, so even if the circuit parallel capacitor, Signal acquisition is not any impact. This article mainly for the pull-up resistor on how to avoid interference with the microcontroller introduced, is being disturbed by the microcontroller interference friends may wish to spend a few minutes to read, I believe will be harvested.
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