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I've just been dabbling for the first time into circuit design with microchips and I noticed a lot of designs put 2.2K or 4.7K resistors on some input lines. I get that this is to limit the potentially damaging current but I don't quite get the math and how it relates to a data spec sheet. For example, the chip AD9984A by Analog Devices has a SDA & SCL pin input for I2C communication; and the data sheet says it is for 3.3V CMOS and Logic High Voltage min is 1V and Logic Low Voltage Max is 0.8V w/ high Max current of -1uA and high Low current of 1uA. When I look at a PCB utilizing this board there is a 2.2K resistor to each of those inputs from the pin-through for the I2C device. Say the I2C device is 5V signals, how is the 2.2K resistor protecting the line and guaranteeing I will still fall in the spec parameters, mathematically? Thanks in advance!