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Tektronix TDS744 CRT to LCD color converter FPGA module DIY

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ltarjanyi75:
Thanks! The board could be made even more compact by removing the reset button, oscillator and JTAG/config pins in the final design. I could have also thought of including some debug pins/leds at the beginning. These would come handy now...

I have compiled your code also with some necessary modifications because of the difference of Spartan 3 (or the lack of my fpga development knowledge) and tested it. Now the background is perfect, but I still have issues with the singal traces: these move slow, have "ghost image", change color and also disappear sometimes from the screen. I don't now if it could be because of the difference between Spartan 3 and 7 versions...

If anyone with more experience in VHDL/FPGA development could help what could be the problem, that would be great! :)

TerrySt:
I can't imagine what would cause slow moving or ghost image traces in the LCD.  Are you sure it is not just a setting on the o'scope?  Like variable persistence or similar?

Terry

Tantratron:

--- Quote from: ltarjanyi75 on December 29, 2023, 07:05:11 pm ---I still have some issues with the result (some random pixel noise, strange color changes and some issues with graph colors), but at least I see something on the LCD.

Also the contact of the PLCC socket is still not the best. At first attempt my image on the screen had some red pixel noise (can be seen on one of the pictures) which somehow disappeared after I pushed the board a bit more to RAMDAC.

--- End quote ---


--- Quote from: ltarjanyi75 on December 29, 2023, 10:45:19 pm ---I have compiled your code also with some necessary modifications because of the difference of Spartan 3 (or the lack of my fpga development knowledge) and tested it. Now the background is perfect, but I still have issues with the singal traces: these move slow, have "ghost image", change color and also disappear sometimes from the screen.

--- End quote ---

Great work and progress Lazlo,

As for the strange persistence or signal issues which you mentioned in this post and previous one. Please check but I think you are using InstaVu or later DPO mode so undo this mode which might solve the issue.

Albert

ltarjanyi75:
Yes, the InstaVu was turned on, which also can be seen on my pictures. I must have been tired when I tried it yesterday...
Now the traces are ok, no slowness or ghost image.
 
The only remaining issue I have, that changing the display setting does not always work correctly: waveform colors are changing even if for example I select the same display color scheme multiple times + sometimes the waveforms totally disappear (which appear again after I change a few times the display settings again). Maybe the waveform disappear is also the result of color change.

Terry, does your display setting change work correctly?
 

TerrySt:
I had that problem a lot when I was having noise issues on my first revision of the board.  I also had it some when using Vincent's VHDL code.  But with my new board and my new VHDL code, it is 100% stable.
It sounds like there is noise or ringing on the /WR signal or possible the data (D0-D7)  or Register Select (RS0-RS2) signals.  The register selects are latched in on the falling edge of /WR.  Then the data is latched in on the rising edge of /WR.  The /WR signal is only active when a color change is sent from the o'scope.   The 25MHz read clock is not used during the color changes.  Take a look at all of the signals and see if they look noisy or have bad ringing on the edges.  You may find that just putting the o'scope probe on one of the signals improves the situation. 
Look to see that the RS signals are stable when the /WR goes low, and that the Data signals are stable when the /WR goes back high.

Terry

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