Electronics > FPGA

FPGA VGA Controller for 8-bit computer

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nockieboy:
Uhh, I'm clearly missing something or doing something wrong, I can't get valid video output at all.  I've got the project set up as you said, then amended GPU_DECA_DDR3_top.sv and BHG_vpg.sv for 720x480 output, but what am I missing?

BrianHG:
You are running the PLL at 148.5MHz.
That's 330Hz progressive at 720x480.
Can your monitor show that?
I know mine cant.
Inside PLL.v you have:

--- Code: --- altpll_component.clk0_divide_by = 100,
altpll_component.clk0_duty_cycle = 50,
altpll_component.clk0_multiply_by = 297,

--- End code ---
That's 50MHz divide by 100=0.5Mhz, multiply by 297=148.5MHz.
Try changing the divide by to 50 and the multiply by to 27.

BrianHG:
Also, for my module BrianHG_display_rmem settings, you may use 640x480 and also set the .DISP_bitmap_width to 640.  This way, the bitmap and display res will be compatible with your current 640x480 settings except you will see a little repeat of the bitmap on the right hand side of the screen.

nockieboy:
Yeah, that's it.  Knew I'd missed something. ::)

BrianHG:
Ok, that looks correct.

Next, we can move to 8 bit pixels.

This means changing how 'BHG_vga_generator' addresses the output of the 'Line_Buffer_DP_ram', going from 32bits down to 8 bits.

Then, taking that 8 bits and piping it through a second 256 word x32bit rom/altsyncram with .mif file containing your palette and for now, let's ignore the incurred 2 pixel delay unless you want to go ahead and fix that.  (We will be changing this module anyways into the new MAGGIE & BART, so don't worry about the fine details...)


Next, wire in the Z80bus to the DDR3.

Then wire in the geometry unit to the Z80 bus and DDR3.
Now, you should have your first accelerated 640x480 256 color display working on your Z80.

You may then upgrade your resolution to 1280x720, IE 720p.

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