SE-VGA/old/vgaout.sv

/******************************************************************************
 * SE-VGA
 * VGA video output
 * techav
 * 2021-04-06
 ******************************************************************************
 * Fetches video data from VRAM and shifts out
 *****************************************************************************/

`include "vgashiftout.sv"

module vgaout (
    input wire          pixClock,
    input wire          nReset,
    input logic [9:0]   hCount,
    input logic [9:0]   vCount,
    input wire          hSEActive,
    input wire          vSEActive,
    input logic [7:0]   vramData,
    output logic [14:0] vramAddr,
    output wire         nvramOE,
    output wire         vidOut
);

wire vidMuxOut; // pixel data shift out
wire vidActive; // combined active video signal

wire nVidLoad;  // Load VRAM data into shifter
vgaShiftOut vOut(
    .nReset(nReset),
    .clk(pixClock),
    .nLoad(nVidLoad),
    .parIn(vramData),
    .out(vidMuxOut)
);

always_comb begin
    if(hCount[2:0] == 0) nVidLoad <= 0;
    else nVidLoad <= 1;

    // combined video active signal
    if(hSEActive == 1'b1 && vSEActive == 1'b1) begin
        vidActive <= 1'b1;
    end else begin
        vidActive <= 1'b0;
    end

    // video data output
    if(vidActive == 1'b1) begin
        vidOut <= ~vidMuxOut;
    end else begin
        vidOut <= 1'b0;
    end

    // vram read signal
    if(vidActive == 1'b1 && hCount[2:0] == 0) begin
        nvramOE <= 1'b0;
    end else begin
        nvramOE <= 1'b1;
    end

    // vram address signals
    // these will be mux'd with cpu addresses externally
    vramAddr[14:6] <= vCount[8:0];
    vramAddr[5:0]  <= hCount[8:3];
end
    
endmodule