The differential receiver of the SN65HVD1176 device is failsafe to invalid bus states caused by the following:

• Open bus conditions, such as a disconnected connector
• Shorted bus conditions, such as cable damage shorting the twisted-pair together
• Idle bus conditions that occur when no driver on the bus is actively driving

In any of these cases, the differential receiver will output a failsafe logic-high state so that the output of the receiver is not indeterminate.

Receiver failsafe is accomplished by offsetting the receiver thresholds such that the input-indeterminate range does not include zero volts differential.

To comply with the RS-422 and RS-485 standards, the receiver output must output a high when the differential input VID is more positive than +200 mV, and must output a low when V_ID is more negative than –200 mV. The receiver parameters that determine the fail-safe performance are V_IT(+) and V_IT(–).

As shown in Section 6.5, differential signals more negative than –200 mV will always cause a low receiver output, and differential signals more positive than –20 mV will always cause a high receiver output. Thus, when the differential input signal is close to zero, it is still above the maximum V_IT(+) threshold of –20 mV, and the receiver output will be high.