de0-zx-spectrum/spectrum.v

module spectrum(input CLOCK_50,
                output wire[7:0] LED,
                output wire[33:0] GPIO_0);
    
    
    // ROM, 16K
    wire[7:0]  rom_data;
    rom0 rom(
		.address(A),
		.clock(CLOCK_50),
		.q(rom_data)
    );
    
    
    reg [15:0] A;                 // Global address bus
    wire [7:0] D;                 // CPU data bus
    wire [7:0] ram0_data;         // Internal 16K RAM data
    wire RamWE;
    // assign RamWE = A[15:14] == 2'b01 && nIORQ == 1 && nRD == 1 && nWR == 0;
    assign RamWE    = 0;
    
    // VRAM, 16K
    wire[12:0] vram_address;
    wire[7:0] vram_data;
    ram16 ram0(
		.clock(CLOCK_50),
		
		.address_a(A[13:0]),
		.data_a(D),
		.q_a(ram0_data),
		.wren_a(0),
		
		//	.address_b({1'b0, vram_address}),
		.address_b(A[13:0]),
		.data_b(8'b0),
		.q_b(vram_data),
		.wren_b(0)
    );
    
    // Rest of RAM, 32K
    wire[7:0] ram1_data;
    ram32 ram1(
		.clock(CLOCK_50),
		
		.address(A[14:0]),
		.data(D),
		.q(ram1_data),
		.wren(0)
    );
    
    
    reg[21:0] counter;
    always @(posedge CLOCK_50)
    begin
        counter <= counter + 1;
        if (counter == 0)
        begin
            A <= A + 1;
        end
    end

	// make the leds blink with rom and ram0 data
    assign LED[3:0] = rom_data[3:0];
    assign LED[7:4] = ram0_data[7:4];
    
	// expose memories at A to GPIO_0
    assign GPIO_0[7:0]   = rom_data;
    assign GPIO_0[15:8]  = ram0_data;
    assign GPIO_0[23:16] = ram1_data;
    assign GPIO_0[31:24] = vram_data;
    
endmodule