I'm in same trouble .I have a PCIe 8431/8 card and I want to put bias resistor on it .But I could not understand on which pad do I have to use for soldering the resistor.Could you please help me about the pad ID of bias resistors?I think the marking on PCB "UL94V-0 198108B-02 "gives you idea about the version of the PCB.
I have a Serial/RS-232/RS-485 Isolated , It seems that National Instruments never release a manual or a simple PDF for resistors location on these boards.
Strange, a company that produce tons of documentation actually do not know the way the 16 pads for resistors are to be set in that board.
I have ask to NI Italy support and they where not able to answer, just the suggestion to look at the very generical document on Seriallike this one http://www.ni.com/pdf/manuals/373096a.pdf.
I had place a similar request to NI support in 2007 and had the same answer: nothing !
Next time before buying a NI product I will think twice....
Anyway i suppose looking at the board that locations XR1,XR2,XR3,XR4 are for termination of each port so the other resistors pads should be for bias.
I was wrong the resistors pads on the board are ONLY for the bias, put 620Ohm resistors everywhere and it should be ok,The termination resistors must be installed externally the board . This was the information I have received from italian NI support
You are replying to a almost 10 years old thread. !!
A RS-485 line should be terminated at both end with a resistor of 120 Ohm (or similar value)