Altera_Forum
Honored Contributor
7 years agoQuartus 2 and .LVDS
I have an easy question for one of the experts. I am using Quartus 2 13.1 and trying to program a Terasic DE3. This is the board with the 4 HSTC connectors, connected to the pads that support LVDS. Here's what I did:
In Verilog I instantiate an input that will come in as LVDS, and an output that goes out single ended on a QPIO pin (to be viewed on a logic analyzer) in the top level module top.v module top ( output qpio, input top ); assign qpio = top; endmodule I then select Processing/Start/Start Analysis & Elaboration and then go into the Pin Planner. I set the pin for the input pin "top" to a legitimate differential pin, and set the I/O Standard to LVDS. The Pin Planner automatically inserts the negative pair for that pin also as LVDS, which is what I expect. I also select the pin for "qpio" as 3.3V. So far so good. When I compile it, it works fine. However, I also want to set the internal resistance to 100 Ohms. So I look in the Pin Planner, and there's a column called "Input Termination", which looks promising, but when I click on it to see what the options are, all I see are things like "Off", "Parallel 50 Ohm with Calibration", then a bunch of "Series 25 Ohms..." options, 40, 50, and 60, but that's it, nothing that says "100 Ohms" or the option "Differential", which is what I had expected. How do I get it to put 100 Ohms across the pair? Also, is it correct that I do not need to instantiate a differential IO buffer in my Verilog? I'm assuming that is the case, since there is no "n" input to route to it anyway.