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Interfacing with Differential Signals with Arty


Question

I am trying to receive 4 and drive 4 differential (rs-422) signals with an Arty board at a rate of 8 Mbit/s. These signals are going to be used in a noisy environment (which is why they are differential).

I noticed that the Arty board's high speed i/o pins (PMOD JB and JC) "have their data signals routed as impedance matched differential pairs" according to the reference manual. Does this mean I would be able to use them as such with no further hardware required? What sort of precautions would I need to take to ensure that I do not damage any hardware and is there example code somewere, preferably in verilog?

In the event that I need an external board to drive/receive the signals for me, is there a pre-built one I could use? I noticed the PMODRS485, but it says that it uses the UART communication protocol which the sending/receiving devices cannot use (they only accept the "raw" signal). If I simply drive the Tx and Rx signals manually can I avoid using the UART protocal? If not, is my best option to breadboard a transceiver?

Thank you in advance.

Edited by Nicholas
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You are correct that the High-Speed Pmod ports are routed as differential pairs. If used in this way you need to ensure that shorts will not occur and that the voltage of the pins does not exceed 3.3 V (VCC on the Arty). Using the PmodRS485 in the manner that you describe will not work as the RX pin can not be driven by the device.

If you want to work at higher line voltages I recommend obtaining a discrete RS422 transceiver connected to the High-Speed Pmod ports.

BKallaher

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