Error ID 176714, false interpretation of differential pairs

[Altera_Forum]

Hello everyone, 

As the title states when I compile my project I receive the Error 176714: pin <name> is assigned to location <name> and pin <name> is assigned to location <name>. these two pins form a differential pair. however, these two locations do not belong to the same differential pair. I assume to know, why it is occuring and am looking for help to prevent this. My project contains a block whichgenerates a certain sequence of 1s and 0s (what else, duh?) which will tell an external analog-digital converter (ADC) what to do. There are four of these blocks as I have four ADCs on my PCB. For future reference, the signals are called SCK1 to SCK4. These signals are being transmitted via LVDS, so in the Pin Planner I assigned some LVDS Pins to SCK1, SCK2, SCK3 and SCK4 (3R emulated LVDS). Due to layout design I had to invert the LVDS signal of SCK4 physically on the PCB. In return I want to invert the SCK4 software wise to compensate. So when I insert an inverter block between the output of the sequence generator block and the pin SCK4, Quartus will promt the error above saying that SCK2 and SCK4 are forming a differential pair. Of course the physical pins won't match and don't belong to the same differential pair. What I tried: 1. When not connecting the sequence to SCK2 the error does not occur. Not even between SCK1 and SCK4 or SCK3 and SCK4 though being exactly the same sequence. 2. When not using the inverter (and thus sending a false message to the ADC) the error does not occur. 3. When I send the sequences phase shifted (so not starting at the same time) for every ADC the error does not occur.  To me it seems like Quartus knows that the sequence of SCK4 is the inverted form of SCK2 and somehow assumes that I want them to be a corresponding LVDS pair. I don't. I have also found this thread where the OP concludes to the same: http://www.alteraforum.com/forum/archive/index.php/t-50319.html  Hopefully someone can help me here! :)  Moe