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In an attempt to solve this problem, I was cross-checking my connections several times. During this, I thought it will be interesting to see the DALI signal coming out of WAGO DALI Module as opposed to the signal coming out of my board. I was surprised to see that, the DALI signal voltage range from WAGO DALI module is very low compared to what is given in the standard. I was expecting a signal range like (18V HIGH - 0V LOW [with appropriate tolerance]) but I got something around 1.7V.

Expected Signal Range

enter image description here

Now, I am wondering if my power supply connection and understanding is correct at all! and I want to understand the basic DALI signal flow between DALI PHY and DALI Slave. Here with the WAGO Module, I am using 18Vdc, 1.1A 787-1007 module as the power supply.

Q1.I could not exactly understand how and why is this voltage level stepping down from 18V to the range of ~1.5V.

This is how the Wago DALI Multi-Master Module block diagram looks like enter image description here

Q2. How is the current limiting to 250mA carried out in the above circuit?

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First you should check that your scope settings match your probes regarding probe attenuation eg 1x, 10x. Second you should detach any other loads from the PSU to see if voltage goes back up when unloaded.

Q1. Maybe the PSU module 787-1007 is damaged due to it being used as a DALI bus power supply when it is not such a thing - it is a power supply for the 753-647 DALI multimaster module. See Page 14, section 3.1 of the 753-647 datasheet - "These power supplies do not provide direct power to the DALI bus, but only indirect power supply via the DALI Multi-master Module". This means you connect the DC output of the 787-1007 to the U pins on the 753-647, and take the DALI signal from that module. See section 6.3.2.2 for wiring diagram.

Q2: The current limiter isn't shown in that diagram but is in the 753-647 module.

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