Problems with Composite video generation

Status
Not open for further replies.

Thread Starter

PauloConstantino

Joined Jun 23, 2016
266
Hi friends,

Firstly, I don't have schematics for my question. If you want to see schematics then please don't reply. If you otherwise would like to help, please read on.

I have finished a circuit that generates composite video and it's almost*** working perfectly. Apart from some ultra weird problem that is occurring when data is displayed. Basically the system sweeps the RAM from address 0 to a certain final address. Each line is 8 pixels in height. Basically it displays 6 lines, and then suddenly it stops displaying, then after a few lines, it starts displaying again.

I have checked the logic of my circuit and everything seems fine. I'm outputting VSYNC for 4 lines. Each line is 0.64us. So VSYNC is 256us long.

Each line has 4.5us HSYNC, and a few microseconds blank. At the end of a line, more blanks are added.

I am using a shift register that is loaded every 8 bits, and then clocked at 8MHz to display the pixels. It seems the shift register is not loading sometimes. Yet my logic for its loading is correct. Has this problem ever occurred with you? Do you have any ideas what this could be? Or any ideas of how I could troubleshoot this? I really don't know what to do anymore. I've checked all connections and theyre all fine.

Here's a photo of what the TV is displaying right now. As you can see it goes nutty after 6 lines. It does look like a logic problem, that is, the shift register loading logic is flawed, but I have checked it and rechecked it and it seems correct.

I appreciate your help, but I don't have schematics for this as I built it from my mind on a breadboard. And no, the problem is not the breadboard.

 

bertus

Joined Apr 5, 2008
20,889
Hello,

We are not mindreaders, so please try to post a schematic.
Without a schematic we can not help you.

Bertus
 

MrChips

Joined Oct 2, 2009
22,113
I appreciate your help, but I don't have schematics for this as I built it from my mind on a breadboard. And no, the problem is not the breadboard.
The problem is obvious then. If there is no problem on the breadboard then the problem is in your mind.
Sorry, we can't help you there.
 
Status
Not open for further replies.
Top