Serial communication through a ADG725

Hi Anders,

See answers to your questions below:

• The ADG725 has a bandwidth of 34 MHz, therefore it should work correctly with a 10 Mbps two-way serial communication protocol (RS485).
• From the description of the issue you have given, the correct behavior of the switch is occurring when the sensor response is returned to the PC i.e. (through the microcontroller), but for some reason when communication occurs on the RS485 line all sensors are receiving and transmitting a response.

In order to try and identify the issue would you be able to give more information on the following:

• The DA and DB lines when RS485 communication is triggered (i.e. scope shots etc.)
• The 2-wire RS-485 transmission network between the ADG725 and RS485 input, was this circuit implemented referencing a design guide ? ( There seems to be no termination resistor present in your network design, it's best practice that each end of the network has a termination resistor equal to the characteristic impedance of the cable.)

Kind regards,

Kevin

Hi

Thanks for your response .

I fixed the issue by making 4 changes.

1. I added a 120Ohm termination resistor at the exit of each multiplexer output.
2. I added a 120Ohm termination at the input of my PCB.
3. I connected my USB-to-RS485's ground to my PCB's ground.
4. One of the two sensors I used to test the PCB was weird so I substituted it for another.

It now works flawlessly (at least for now).

I hope my paint skills are adequate.

Hi Anders,

Great to see that the additions you made to your circuit helped solve the issue.

Please don't hesitate to contact, if you need any further assistance.

Regards,

Kevin

Hi Anders,

Great to see that the additions you made to your circuit helped solve the issue.

Please don't hesitate to contact, if you need any further assistance.

Regards,

Kevin