• rehsd

VGA from Cmod A7 Working

Updated: Feb 11


Update: I have it working. See postscript at the bottom of this post.


I am attempting to get the Arty Pmod VGA Demo running on a Digilent Cmod A7 to see if the Cmod is able to drive basic VGA (e.g., 640x480). I haven't been able to get this working yet and am looking for insight on what I might be overlooking.


I have started a new project in Vivado and am using the VHDL sample file provided from Digilent. I have configured the VHDL and clocking wizard for 640x480 output. I have configured constraints in the XDC file. I have made connections as seen in the images below. I am getting (what I think are) reasonable vertical and horizontal sync outputs, yet my monitors (have tried a couple) won't sync to the signal.


My primary question is whether this type of setup should theoretically work, or if I'm barking up the wrong tree. If this likely should work, any thoughts on what I am overlooking? I expect the jumper wires aren't great for signal quality, but hopefully that's not what's derailing this setup. Also, I am feeding power from the Pmod connector on the Cmod to the breadboard rails and then to the PmodVGA; power looks fine (3.53V) at the PmodVGA pins. The SN74ALVC245 ICs on the PmodVGA should have no issues under 3.6V.

Connections (you will be shocked to learn that I did not go to art school)
Connections (you will be shocked to learn that I did not go to art school)

Config in VHDL
Config in VHDL
Clock config
Clock config
Constraints
Constraints

Output of horizontal and vertical sync, measured at the test point header:



Postscript

Even though I *triple-checked* the connections, I somehow still managed to have the pigtails on the Pmod connector backwards (top vs. bottom, not left vs. right). I was able to track down that frequencies going into the VGApmod looked fine, but frequencies coming out of the VGA D-Sub connector were whacky.


Here it is running 800x600:



Next... MicroBlaze control of the video output from the Cmod A7.


Continued: Cmod A7 FPGA : Video Test Pattern Generator.

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