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//============================================================================
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//============================================================================
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// Implementation of the ZX Spectrum keyboard input generator
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// ZX Spectrum keyboard input
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// This module takes scan-codes from the PS/2 keyboard input and sets
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//
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// corresponding ZX key bitfields which are read by IN (FE) instructions.
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// This module takes scan-codes from the attached PS/2 keyboard and sets
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// corresponding ZX key bitfields which are read by the 'IN' instructions.
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//
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//
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// PS/2 | ZX Spectrum
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// PS/2 | ZX Spectrum
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// ----------+-----------------
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// ----------+-----------------
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// CTRL | CAPS SHIFT
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// CTRL | CAPS SHIFT
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// ALT | SYMBOL SHIFT
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// ALT | SYMBOL SHIFT
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//
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//
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// In addition to regular alpha-numeric keys, this code simulates many standard
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// For convenience, in addition to regular alpha-numeric keys, this code
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// symbols on the PS/2 keyboard for convenience.
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// simulates several other standard symbols on the PS/2 keyboard.
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//
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//
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// PS/2 | ZX Spectrum
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// PS/2 | ZX Spectrum
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// ----------+-----------------
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// ----------+-----------------
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// BACKSPACE | DELETE
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// BACKSPACE | DELETE
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// Arrows Left, Right, Up, Down
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// Arrows Left, Right, Up, Down
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// ESC | BREAK (CAPS+SPACE)
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// ESC | BREAK (CAPS+SPACE)
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// SHIFT => PS/2 shift for these separate additional keys: -_ += ;: "' <, >. ?/
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// SHIFT => PS/2 shift for additional keys: -_ += ;: "' <, >. ?/
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//
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//
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// Copyright (C) 2014-2016 Goran Devic
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// Copyright (C) 2014-2016 Goran Devic
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//
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//
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// This program is free software; you can redistribute it and/or modify it
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// This program is free software; you can redistribute it and/or modify it
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// under the terms of the GNU General Public License as published by the Free
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// under the terms of the GNU General Public License as published by the Free
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// 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
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// 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
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//============================================================================
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//============================================================================
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module zx_keyboard
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module zx_keyboard
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(
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(
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input wire clk,
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input wire clk,
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input wire reset, // Reset (negative logic)
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input wire nreset, // Active low reset
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// Output ZX-specific keyboard codes when requested by the ULA access
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// Output ZX-specific keyboard codes when requested by the ULA access
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input wire [15:0] A, // Address bus
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input wire [15:0] A, // Address bus
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output wire [4:0] key_row, // Output the state of a requested row of keys
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output wire [4:0] key_row, // Output the state of a requested row of keys
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// Calculate a "key is pressed" signal
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// Calculate a "key is pressed" signal
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assign pressed = ~(&keys[7] & &keys[6] & &keys[5] & &keys[4] & &keys[3] & &keys[2] & &keys[1] & &keys[0]);
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assign pressed = ~(&keys[7] & &keys[6] & &keys[5] & &keys[4] & &keys[3] & &keys[2] & &keys[1] & &keys[0]);
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// Output requested row of keys continously
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// Output requested row of keys continously
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always @(*) // always_comb
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assign key_row =
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begin
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(~A[8] ? keys[0] : 5'b11111) &
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case (A[15:8])
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(~A[9] ? keys[1] : 5'b11111) &
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8'b11111110: key_row = keys[0];
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(~A[10] ? keys[2] : 5'b11111) &
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8'b11111101: key_row = keys[1];
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(~A[11] ? keys[3] : 5'b11111) &
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8'b11111011: key_row = keys[2];
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(~A[12] ? keys[4] : 5'b11111) &
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8'b11110111: key_row = keys[3];
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(~A[13] ? keys[5] : 5'b11111) &
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8'b11101111: key_row = keys[4];
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(~A[14] ? keys[6] : 5'b11111) &
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8'b11011111: key_row = keys[5];
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(~A[15] ? keys[7] : 5'b11111);
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8'b10111111: key_row = keys[6];
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8'b01111111: key_row = keys[7];
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default:
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key_row = 5'b11111;
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endcase
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end
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always @(posedge clk or negedge reset)
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always @(posedge clk or negedge nreset)
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begin
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begin
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if (!reset) begin
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if (!nreset) begin
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released <= 0;
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released <= 0;
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extended <= 0;
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extended <= 0;
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shifted <= 0;
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shifted <= 0;
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keys[0] <= '1;
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keys[0] <= '1;
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