Video DAC ADV7123 related

[garimella]

Few queries on Video DAC interfacing with FPGA
1. What should be clock frequency selected for FPGA to drive VGA. I suppose it depends on resolution. But any guide that helps to choose between resolution vs frequency.

2. HS and VS signals are usually odd frequencies, how to generate them from FPGA.

3. I am also looking for layout guidelines for Video DAC ADV7123.

 

[barry]

1) the DAC comes in three different speed grades, THATS what's going to determine the required FPGA clock
2) you also have to be concerned about your pixel clock. All three are related. But not sure I understand the question. You are creating your own VGA interface? You need some complex code.
3) there are layout guidelines in the data sheet. Perhaps the mfr has an eval board, you could copy that layout.

 

[garimella]

How to interface MCU with video DAC?

 

[barry]

How to interface MCU with video DAC?

I thought you were using an FPGA. Is this a different question? If so, it's pretty broad. Do you have a specific question?

 

[garimella]

I have some more questions and I will refine what I asked eariler M
1. MCU interfaces with FPGA and FPGA interacts with video DAC. In order to display meaningful info in VGA monitor, I am planning to dump the data from MCU to VGA via FPGA. Wanted to know interface strategy from MCU to FPGA

2.My second question is related to understanding timings of VGA. It is very confusing. I was trying to correlate the functioning of CRT oscilloscope and LCD monitor. As I understand signal of interest (say sine wave) is given to vertical deflection plates and Horizontal sync is also simultaneously applied to display sine wave with reference to time axis (explained in the link https://www.tpub.com/neets/book16/71b.htm). In CRT horizontal deflection signal is a sawtooth wave

Now coming back to VGA signals, it has two signals Hsync and Vsync, which are in the form of digital pulses. How do they work with reference to concept of CRT mentioned above. Do the incoming video signals get converted to Vsync? What happens to Hsync then?

 

[KlausST]

Hi,

Don't mix a scope CRT with a VGA monitor.

Please focus on your application.
Please tell where does the picture information come from. Is it text or still picture ir movie?
Who sets the frame rate?
What memory? Is there some picture data processing necessary?

VGA general: there are a lot of documents and web pages available that describe VGA signals an their timing.

Klaus

 

[garimella]

Ok. I want to interface keyboard to MCU and the display the characters typed on VGA. This design has MCU@20MHz interfaced to FPGA. FPGA connects to Video DAC. Now let me understand, how to accomplish this task.

 

[barry]

There are MANY ways to do this. You could have a parallel interface from MCU to FPGA; you could use SPI or I2C. Basically, you want to send characters to the FPGA. It would be simple to just have an 8-bit bus and a strobe.

But don't you need to create a video frame? Are you just going to send characters one at a time to the display? I think you need a little more definition of exactly what you're trying to do.

 

[garimella]

For the time being I would like to send characters typed on keyboard to display on the monitor. I want to understand how to display say Character "A" on VGA through FPGA-Video DAC. Example will help. I am clear with MCU FPGA interface.

 

[barry]

For the time being I would like to send characters typed on keyboard to display on the monitor. I want to understand how to display say Character "A" on VGA through FPGA-Video DAC. Example will help. I am clear with MCU FPGA interface.

Not good enough.

Do you want display one and only one character? If you send two characters, do you want them to display next to each other? What if you send 200 characters?

You need to educate yourself on the VGA protocol before you go much further.

 

[garimella]

Ok I will make it clear. Yes I would like to display series of characters limited to 10 Max. The example I gave ("A") is is only indication. I wanted to begin somewhere and add up if I succeeded. The characters have to be displayed next to each other. ( eg "ABCDEFGHIJ")

 

[barry]

You seriously need to learn about the VGA interface, and that can't be done here; there's plenty of information on the web. Basically, you need to create a frame buffer in FPGA memory. Your vga module will read each memory element (pixel RGB values) and generate the HS and VS signals based on your display configuration.

 

[ads-ee]

Read some links like this (via Google "fpga vga"):
https://www.fpga4fun.com/PongGame.html
https://eewiki.net/pages/viewpage.action?pageId=15925278
https://www.eetimes.com/document.asp?doc_id=1274613

Those are the first 3 links that show up when I searched for "fpga vga". All three of them have information on timing and code that should be pretty easy to follow.