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Testing PmodRS485 to convert a single ended SSI signal to differential



Hi, I'm currently working on a system that uses an AMS AS5040 Rotary Encoder that is configured with SSI. I'd like to read this encoder using a PLC that uses an RS422 SSI encoder input block. The main problem with this is that the encoder outputs a single ended signal, whereas the SSI block requires a differential RS422 signal. The minimum baud rate is 125kbps. 

The encoder only has two signals that are important to the project. There is a clock input signal and a data output signal.  

In order to convert the single ended data signal to differential/RS422, I bought some of your PmodRS485 modules. I wanted to test the device before connecting it to my system, so I designed a test setup using a function generator. I only intend to use the transmit data functionality. Here is how I connected the device for the test:

RE - Ground

TxD - Function Generator + 

RxD - NC

DE - 5V

GND - Function Generator - (connected to ground) 

VCC - 5V

All of the grounds were connected together. I then send a 10hz 0-5V square wave into the function generator. However, I did not see the correct outputs from the Z (inverted) and Y (noninverted) signals. I was reading nearly 0V for both signals with respect to ground (a few millivolts each). I also tested 1000hz and didn't see any difference. 

I was expecting to see the identical function generator signal on channel Y and the inverted signal on channel Z. Is my setup incorrect? Could you please let me know how I can test this device for proper functionality using the TxD/transmit data mode? 

One thing that I might have done wrong is that I soldered wires directly onto the pins (opposite side to the screw terminals), because I didn't have the correct connector. Could this have damaged the board? What type of sockets does this connect with? Please let me know if you need any more information. 

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I have a similar situation, and wondering if this problem has been solved. 

In addition to the above connection, I connected function generator- signal to PmodRS485 GND.

Any advice is appreciated.

Thank you,



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