URL
https://opencores.org/ocsvn/a-z80/a-z80/trunk
Subversion Repositories a-z80
[/] [a-z80/] [trunk/] [host/] [basic_nexys3/] [basic_nexys3_fpga.v] - Rev 20
Go to most recent revision | Compare with Previous | Blame | View Log
//============================================================================ // Host design containing A-Z80 and a few peripherials // // This module defines a host board to be run on an FPGA. // // Copyright (C) 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 CLOCK_100, input wire KEY0, // KEY0 is reset input wire KEY1, // KEY1 generates a maskable interrupt (INT) input wire KEY2, // KEY2 generates a non-maskable interrupt (NMI) output wire UART_TXD, inout wire [7:0] GPIO_0, // Test points output wire [7:0] GPIO_1, output wire [7:0] GPIO_2, inout wire [7:0] GPIO_3 ); `default_nettype none // Export selected pins to the extension connector assign GPIO_0[7:0] = A[7:0]; assign GPIO_1[7:0] = A[15:8]; assign GPIO_2[7:0] = D[7:0]; assign GPIO_3 = {reset, uart_tx, nM1, nMREQ, nRFSH, nHALT, nBUSACK}; // Basic wires and the reset logic wire uart_tx; wire reset; wire locked; assign reset = locked & ~KEY0; assign UART_TXD = uart_tx; // ----------------- CPU PINS ----------------- wire nM1; wire nMREQ; wire nIORQ; wire nRD; wire nWR; wire nRFSH; wire nHALT; wire nBUSACK; wire nWAIT = 1; wire nBUSRQ = 1; wire nINT = ~KEY1; wire nNMI = ~KEY2; wire [15:0] A; reg [7:0] D /* synthesis keep */; //~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ // Instantiate PLL //~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ wire pll_clk; wire clk_uart; // 50MHz clock for UART clock pll ( .CLK_IN1(CLOCK_100), .CLK_OUT1(pll_clk), .CLK_OUT2(clk_uart), .LOCKED(locked) ); //~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ // Clocks //~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ wire clk_cpu = pll_clk; // CPU clock == PLL1 clock // Test code: Divide pll clock with a power of 2 to reduce effective CPU clock // reg [0:0] counter = 0; // always @(posedge pll_clk) // begin // if (counter==1'b0) // clk_cpu <= ~clk_cpu; // counter <= counter - 1'b1; // end // ----------------- INTERNAL WIRES ----------------- wire [7:0] RamData; // Data writer from the RAM module wire [7:0] CpuData; assign CpuData = nRD==0 ? D[7:0] : {nIORQ,nRD,nWR}==3'b011 ? 8'h80 : {8{1'bz}}; wire RamWE; assign RamWE = nIORQ==1 && nRD==1 && nWR==0; wire uart_busy; wire UartWE; assign UartWE = nIORQ==0 && nRD==1 && nWR==0; // Memory map: // 0000 - 3FFF 16Kb RAM always @(*) // always_comb begin case ({nIORQ,nRD,nWR}) // -------------------------------- Memory read -------------------------------- 3'b101: D[7:0] = RamData; // -------------------------------- Memory write ------------------------------- 3'b110: D[7:0] = CpuData; // ---------------------------------- IO write --------------------------------- 3'b010: D[7:0] = CpuData; // ---------------------------------- IO read ---------------------------------- 3'b001: D[7:0] = {7'b0000000, uart_busy}; // IO read *** Interrupts test *** // This value will be pushed on the data bus on an IORQ access which // means that: // In IM0: this is the opcode of an instruction to execute, set it to 0xFF // In IM2: this is a vector, set it to 0x80 (to correspond to a test program Hello World) 3'b011: D[7:0] = 8'h80; default: D[7:0] = {8{1'bz}}; endcase end //~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ // Instantiate A-Z80 CPU module //~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ z80_top_direct_n z80_( .nM1 (nM1), .nMREQ (nMREQ), .nIORQ (nIORQ), .nRD (nRD), .nWR (nWR), .nRFSH (nRFSH), .nHALT (nHALT), .nBUSACK (nBUSACK), .nWAIT (nWAIT), .nINT (nINT), .nNMI (nNMI), .nRESET (reset), .nBUSRQ (nBUSRQ), .CLK (clk_cpu), .A (A), .D (CpuData) ); //~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ // Instantiate 16K of RAM memory //~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ram #( .n(14)) ram_( .addr(A[13:0]), .clk(clk_cpu), .data_in(D), .we(RamWE), .data_out(RamData) ); //~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ // Instantiate UART module //~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ uart #( .BAUD(115200), .IN_CLOCK(50000000) ) uart_( // Outputs .busy(uart_busy), .uart_tx(uart_tx), // Inputs .wr(UartWE), .data(D), .clk(clk_uart), .reset(!reset) ); endmodule
Go to most recent revision | Compare with Previous | Blame | View Log