KNX, DALI, RS-485 Modbus/mstp voltage


I work with BUS systems in building automation. And I think the Saleae Logic looks like it could give us more info when we are troubleshooting on modbus lines and BacNet mstp lines.

But If I understand the correct it’s a max voltage of 25 Volt. So I can’t use it on a KNX BUS.

In KNX TP the bus cable supplies all bus devices with both data
and power. The rated voltage of the bus system is 24 V, while
the voltage provided by the power supplies is 30 V. The bus
devices work without error at voltages between 21 V and 30 V,
so a tolerance range of 9 V is available to compensate for volt-
age drops in the cable, and contact resistance.

But Dali Bus would work, they use from 16 V DC to max 22,5V DC.

I found some info on the webpage. But the read more below don’t give much info

Are there any one that uses the Saleae Logic on Dali or KNX?


@espenbo Thanks for writing in!

First, I’m not sure how you reached that support article you shared, but the correct link is below. I’ll make sure to take the one you shared down.

We’ve received requests to support decoding DALI mode, which we’ve recorded below.

We unfortunately don’t have experience with DALI or KNX however. Hopefully the support article I shared above provides some more details on our recommendations around decoding differential signals!

Thanks for your feedback.
As I understand it then we should have a voltage divider on modbus RS-45 lines, knx and dali.
I tried searching for this but found mostly wiring diagrams. Does anyone have any links to good voltage divider 30 V. For use with KNX, dali.

If you would like to make support for KNX I would recommend Elsner elektronik. Get in touch with Bastian

They develop KNX equipment and is probably interested in your product as well.

@espenbo Sorry I can’t provide much help with recommending specific resistor divider values given my inexperience with DALI / KNX. However, when doing so, you’ll want to keep in mind the input impedance of our Logic devices, which can be found in our datasheets below.