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What are invalid RS-232 receiver input levels, and how do they occur?

April 26, 2017input invalid levels occur receiver RS-232

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What are invalid RS-232 receiver input levels, and how do they occur?

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A receiver input voltage between 0.3V and +0.3V is considered invalid, while a voltage greater/less than +/-2.7V is considered valid. Voltages between these are indeterminate and may or may not cause power down. Invalid receiver levels occur when the RS-232 cable disconnects (receiver inputs float, but on-chip termination resistors pull receiver inputs to GND), or when the IC driving the receivers powers down.