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I got this IC in my circuit and I'm wondering if I could hook up a pull-up network to it, in the following way:

Since it's an RS485 transceiver, the input to it is differential. I need to know if I can input a non-differential voltage as an input to it.

My intention is to eventually determine the voltage that comes into the IC, if it's high then the cable is not connected and when it's low the cable is connected. (for clearance - the voltage will be determined my an MCU input reading the high/low states).

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Daniel Korbin
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  • Do you still need to be able to communicate with a standard RS485 transmitter, or simply detect the cable? – Justme Dec 07 '20 at 09:23
  • How does the cable change the circuit? What is its voltage? – CL. Dec 07 '20 at 09:27
  • @Justme I'm not interested in what will happen at the output of the IC since there are 4 of those in the circuit and one of them will not be used. I simply need to detect the cable. – Daniel Korbin Dec 07 '20 at 09:29
  • @CL. The cable is an input to the circuit, it will carry a differential voltage (-5V or +5V). I simply need to know if the cable is connected or not, and a way I thought would be possible is by hooking up a pull-up resistor to VCC and read the voltage on an MCU. if the cable is connected, the loop is closed and the MCU will read a logic low and if the cable is disconnected, the MCU should read a logic high. – Daniel Korbin Dec 07 '20 at 09:32
  • You said above that the cable is not differential. I do not understand where you would get a loop. Please edit your question to show exactly how the cable gets connected, and what its possible voltages are. – CL. Dec 07 '20 at 09:46
  • @CL. excuse me, I confused myself and you at the same time. I am free to input a non-differential voltage, as the above figure demonstrates - the input is across the termination resistor. The IC usually expects a differential voltage as its input but I'm wondering if I could simply apply a, let's say, 5V signal through the pull-up resistor as shown in the figure. bottom line is - if what's in the figure is acceptable in terms of not damaging the IC. The main thing is not the IC but the cable, I got to make sure that I know if it's connected or not. is the above figure appropriate? – Daniel Korbin Dec 07 '20 at 10:07
  • What impedance is at the far end of the cable? Is it another RS485 interface? Is it several parallel 485 interfaces? If so how many? – Andy aka Dec 07 '20 at 10:49

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