THVD1520: What's the receiver end status when △VOD reach at 50mV?

Tess Chen,

Thank you for the questions. Per EIA-485 standards, input threshold for RS-485 receiver logic HIGH is >= +200mV, while logic LOW is <=-200mV. This creates a 400mV indeterminate state for the receiver inputs. 

Tess Chen said:

What will happen for the receiver side state if the driver △VOD range is exactly for example △VOD=50mV and VA and VB approximately to 0? 

The output logic on receiver pin "R" on the THVD1520 is undetermined if  -200mV >= VOD = VA - VB <= +200mV (basically saying VOD is within the indeterminate region as depicted in the figure above). So if it were the case the VA = VB = 0, and △VOD=50mV, this data would rest in the indeterminate state.

 TI RS485 devices are designed to always supply a differential voltage between bus lines "A" and "B" during transmission on the bus lines. 

THVD1520 has built  in internal fail-safe biasing. If the transceiver is disconnected from the bus (Open Circuit), bus lines are shorted (short-circuit), or the bus is not actively driven (idle bus), receiver output logic will output HIGH. See table 2. for all receiver output logic states combined with /RE. 

Please let me know if you have any more questions,

Regards,

Tyler