Tweaking the 128×32 LEDDMD Verilog

There was a few problems with the code for the 128×32 LEDDMD. Every so often there was flickering at random spots on the screen. This was because of the way the display memory was updated. I already fixed it by putting a dummy state at the end of the display memory update. Doing so actually increased the speed that data could be sent to the FPGA. There is no waiting between the Latch pulls.

The last problem is that there is some slight ghosting on the screen. Due to the way the screen updates it looks like the Column data is updating slightly before the rows are updated. Because of this you get a ghost effect on the opposite side of the screen that is up one row.

I think the reason why is because there is a slight delay in the rows caused by the decoders. The current plan of attack is to buffer the Column data a couple cycles before outputting.

2 thoughts on “Tweaking the 128×32 LEDDMD Verilog”

  1. With a regular DMD display the ghosting can occur if the display is not briefly shutdown while doing the latch pulls, and/or if the display doesn’t detect a proper row scan pulse (i.e too short pulse).

    Could this be a possible problem for your display as well?

  2. Robert, that was the problem. I made the change in the code. Chris Kraft actually has the DMD now. Ben and I decided to not use this for pinball. Chris is going to make some Display with it.

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