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//============================================================================

// Host design containing A-Z80 and a few peripherials

//

// This module does not define a physical board but is only meant to be

// compiled within the ModelSim host test.

//

//  Copyright (C) 2014-2016  Goran Devic

//

//  This program is free software; you can redistribute it and/or modify it

//  under the terms of the GNU General Public License as published by the Free

//  Software Foundation; either version 2 of the License, or (at your option)

//  any later version.

//

//  This program is distributed in the hope that it will be useful, but WITHOUT

//  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

//  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for

//  more details.

//

//  You should have received a copy of the GNU General Public License along

//  with this program; if not, write to the Free Software Foundation, Inc.,

//  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.

//============================================================================

module host

(

    input wire clk,

    input wire reset,

    input wire nint,

    input wire nnmi,

    output wire uart_tx

);

// ----------------- CPU PINS -----------------

wire nM1;

wire nMREQ;

wire nIORQ;

wire nRD;

wire nWR;

wire nRFSH;

wire nHALT;

wire nBUSACK;

wire nWAIT = 1;

wire nINT = nint;

wire nNMI = nnmi;

wire nBUSRQ = 1;

wire [15:0] A;

wire [7:0] D;

// ----------------- INTERNAL WIRES -----------------

wire [7:0] RamData;                     // RamData is a data writer from the RAM module

wire RamWE;

assign RamWE = nIORQ==1 && nRD==1 && nWR==0;

wire uart_busy;

wire UartWE = nIORQ==0 && nRD==1 && nWR==0;

// Memory map:

//   0000 - 3FFF  16K RAM

assign D[7:0] = (A[15:14]=='h0 && nIORQ==1 && nRD==0 && nWR==1) ? RamData :

                (nIORQ==0 && nRD==1 && nWR==1) ? 8'h80 :

                (nIORQ==0 && nRD==0 && nWR==1) ? {7'h0,uart_busy} :

                {8{1'bz}};

//~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

// Instantiate A-Z80 CPU module

//~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

z80_top_direct_n z80_( .*, .nRESET(reset), .CLK(clk) );

//~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

// Instantiate 16Kb of RAM memory

//~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

ram ram_( .address(A[13:0]), .clock(clk), .data(D[7:0]), .wren(RamWE), .q(RamData[7:0]) );

//~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

// Instantiate UART module

//~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

uart #( .BAUD(115200), .IN_CLOCK(10000000) ) uart_(

   // Outputs

   .busy(uart_busy),

   .uart_tx(uart_tx),

   // Inputs

   .wr(UartWE),

   .data(D[7:0]),

   .clk(clk),

   .reset(!reset)

);

endmodule