Zybo Z7-20

[chiron40k]

Hi,

I'm attempting to connect a VGA monitor to my Zybo. I see that a Pmod is available for this, but I'd like to try to build up that functionality myself.

Given that I'm using 5 of the Pmod 3.3V outputs for VSYNC, HSYNC, R, G, and B how do I select the correct resistors between the output of the Pmod port and the VGA connector? I understand that the RGB pins are rated for 0.7V peak-to-peak and that the expected impedance on these lines is 75 Ohms.

Also, is it necessary to use a bus transciver between the Pmod and the VGA connectors?

Thanks!

Chris

[artvvb]

Hi @chiron40k

There are a fair number of materials around on how to select the resistors. This post looks at the specific circuit on the Pmod VGA: https://electronics.stackexchange.com/questions/473370/is-this-how-a-r-2r-dac-for-vga-should-work. This project also looks comprehensive for a 4-bit DAC: https://svenssonjoel.github.io/pages/zynqberry-vga/index.html

I'm not certain, but suspect that the buffer is there to isolate the DAC circuitry from any resistors that might be in series with the Pmod outputs. The Zybo's "High Speed" Pmod ports don't have these resistors.

Thanks,

Arthur