I want to know if my wiring is correctly . I’m trying to control 9 fvd v20 via USS, I’m using a 3 pole shielded cable p- p+ 0v , the connection between each fvd is directly to terminal buss ( I’m not jumping cable between each fvd) , the cable shield is connected to earth ground from each fvd just in one side , p+ is to db9 3 , p- to 8 and 0v to pin 1. The problem of all this is that I’m not able to communicate with any of the fvd .

Hello Elektrische;

Your design seems strange, you are using multiple point-to-point connections for your VFDs, whereas USS specifies daisy-chain connections.

This document should clarify the USS protocol requirements.

Specification: Universal Serial Interface Protocol USS Protocol

https://support.industry.siemens.com/cs/ww/en/view/24178253

And this application example, shows how USS protocol can be used with a multiple V20 drive.

Simple Control of a SINAMICS V20 with a SIMATIC S7-1200/1500 via USS

https://support.industry.siemens.com/cs/ww/en/view/109480894

Hope this helps,

Daniel Chartier

Special attention to what is required for "termination" of the communication cable. This is mentioned in the documents which Mr Chartier suggested.

Hello Electrische;

Tio add to qwazee's judicious suggestion, you could use the option of Profibus-DP cable and connectors,.This would have the advantage that connectors for Profibus integrate the termination circuit that can be activated through a switch.

Hope this helps,

Daniel Chartier

dchartier

Hello Electrische;

Tio add to qwazee's judicious suggestion, you could use the option of Profibus-DP cable and connectors,.This would have the advantage that connectors for Profibus integrate the termination circuit that can be activated through a switch.

Hope this helps,

Daniel Chartier

The Profibus plug would be most helpful on the PLC side.

The drives is a different matter. It does not have built-in terminations. That means you have to add resistors.

The trouble is that the topic starter is using a star- connected network. That would mean terminating at each drive -- I think. That is a royal mess. Best would be to connect in a bus topology as what the documentation states.

The last time I used the V20, I used the communication board which provides a terminating connection. We bought some already made up terminating resistor boards which you can buy from Siemens. (Picture provided in documentation linked to by Mr. Chartier.)

I opted to use Modbus RTU because of the device count restrictions posed by USS.

I hope these notes will be of value.
Cheers.

Elektrische

The problem of all this is that I’m not able to communicate with any of the fvd .

Well, you don't like daisy-chain connection.

OK, what prevents you from doing things as follows?

1. make connection between CM1241 module and a single drive.
2. prepare respective code.
3. establish communication and get control upon the drive.
4. capture a waveform while data exchanging.

1. connect the next drive as you had desired to the existing pair.
   
2. modify your code in accordance with your alterations at wiring and hardware presence.
   
3. ensure an absence of signal collisions while slave's responding.
   
4. capture a waveform while data exchanging. Make a comparison.

BR