NI 6583 LVDS Receiver State When Disconnected or Not Driven

Updated Jan 17, 2018

Reported In

Hardware

  • NI-6583

Issue Details

With the NI 6583 DIO module, what is returned from the LVDS receiver when the line is disconnected or not being driven by another device?  Is there a guaranteed reading of High or Low?

Solution

The NI 6583 utilitzes the TI SN65LVDM180 LVDS receiver.  This receiver has a built in Fail Safe, and it returns all HIGH values when the line is disconnected(open circuit) or not being driven(high impedance).  When this occurs, the LVDS receiver pulls each line of the signal pair to near VCC through 300-kΩ resistors as shown in the figure below. The fail-safe feature uses an AND gate with input voltage thresholds at about 2.3 V to VCC – 0.4 V to detect this condition and force the output to a high-level, regardless of the differential input voltage.

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