55 lines
2.3 KiB
C#
55 lines
2.3 KiB
C#
using Core.Interfaces;
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using System.Diagnostics;
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using static System.Runtime.InteropServices.JavaScript.JSType;
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namespace Core.Io
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{
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public class IO_Bus
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{
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public byte BorderColorIndex { get; private set; } = 7;
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public bool BeeperState { get; private set; } = false;
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public byte[] KeyboardRows = new byte[8] { 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF };
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public byte ReadPort(ushort portAddress)
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{
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// The Spectrum ULA responds to any even port address (where the lowest bit is 0)
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if ((portAddress & 0x01) == 0)
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{
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byte highByte = (byte)(portAddress >> 8); // The B register!
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byte result = 0xFF; // Start assuming no keys are pressed
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// The ROM pulls a specific bit low (0) in the high byte to request a row.
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// Sometimes it pulls multiple bits low to scan multiple rows at once, so we AND the results.
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if ((highByte & 0x01) == 0) result &= KeyboardRows[0]; // 0xFE: CAPS, Z, X, C, V
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if ((highByte & 0x02) == 0) result &= KeyboardRows[1]; // 0xFD: A, S, D, F, G
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if ((highByte & 0x04) == 0) result &= KeyboardRows[2]; // 0xFB: Q, W, E, R, T
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if ((highByte & 0x08) == 0) result &= KeyboardRows[3]; // 0xF7: 1, 2, 3, 4, 5
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if ((highByte & 0x10) == 0) result &= KeyboardRows[4]; // 0xEF: 0, 9, 8, 7, 6
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if ((highByte & 0x20) == 0) result &= KeyboardRows[5]; // 0xDF: P, O, I, U, Y
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if ((highByte & 0x40) == 0) result &= KeyboardRows[6]; // 0xBF: ENTER, L, K, J, H
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if ((highByte & 0x80) == 0) result &= KeyboardRows[7]; // 0x7F: SPACE, SYM, M, N, B
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// The top 3 bits (5, 6, 7) are unused by the keyboard and usually return 1 on a real Spectrum
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return (byte)(result | 0xE0);
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}
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// Return 0xFF for unhandled ports
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return 0xFF;
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}
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public void WritePort(ushort portAddress, byte portValue)
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{
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// The ULA intercepts any write to an even port address
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if ((portAddress & 0x01) == 0)
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{
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// The bottom 3 bits (0-2) define the border color
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BorderColorIndex = (byte)(portValue & 0x07);
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// Bit 4 controls the speaker
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BeeperState = (portValue & 0x10) != 0;
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// Bit 3 handles the cassette MIC output
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}
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}
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}
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} |