From 968141056b71d5c47809d3a16e4849a403e5f182 Mon Sep 17 00:00:00 2001
From: Marc Parsons <marc@parsons.cc>
Date: Thu, 16 Apr 2026 14:40:05 +0100
Subject: [PATCH] Some minor changes and playing about

---
 Core/Cpu/Z80.cs           |  19 ++++-------
 Core/Io/IO_Bus.cs         |  43 +++++++++++++++++++++++++
 Core/Io/SimpleIoBus.cs    |  20 ------------
 Core/Memory/MemoryBus.cs  |  10 +++++-
 Desktop/48.rom            | Bin 16384 -> 16384 bytes
 Desktop/48.rom.bak        | Bin 0 -> 16384 bytes
 Desktop/DebuggerForm.cs   |  22 +++++++------
 Desktop/Form1.Designer.cs |   1 +
 Desktop/Form1.cs          |  66 ++++++++++++++++++++++++++++++++++++--
 9 files changed, 135 insertions(+), 46 deletions(-)
 create mode 100644 Core/Io/IO_Bus.cs
 delete mode 100644 Core/Io/SimpleIoBus.cs
 create mode 100644 Desktop/48.rom.bak

diff --git a/Core/Cpu/Z80.cs b/Core/Cpu/Z80.cs
index 7ce3dec..d98ddac 100644
--- a/Core/Cpu/Z80.cs
+++ b/Core/Cpu/Z80.cs
@@ -1,5 +1,6 @@
 using System;
 using Core.Interfaces;
+using Core.Io;
 
 namespace Core.Cpu
 {
@@ -38,12 +39,12 @@ namespace Core.Cpu
 
         // The Memory Bus
         private readonly IMemory _memory;
-        private readonly IIoBus _ioBus;
+        private readonly IO_Bus _simpleIoBus;
 
-        public Z80(IMemory memory, IIoBus ioBus)
+        public Z80(IMemory memory, IO_Bus ioBus)
         {
             _memory = memory;
-            _ioBus = ioBus;
+            _simpleIoBus = ioBus;
             Reset();            
         }
 
@@ -122,15 +123,7 @@ namespace Core.Cpu
         // Placeholder for your hardware I/O
         private byte ReadPort(ushort portAddress)
         {
-            // If the port is 0xFE, the ROM is asking for keyboard/tape/ULA data!
-            // For now, we will return 0xFF (meaning "No keys are currently pressed")
-            if ((portAddress & 0xFF) == 0xFE)
-            {
-                return 0xFF;
-            }
-
-            // Default floating bus return
-            return 0xFF;
+            return _simpleIoBus.ReadPort(portAddress);
         }
 
         public int Step()
@@ -1086,7 +1079,7 @@ namespace Core.Cpu
                     // The Z80 puts 'A' on the top 8 bits, and 'n' on the bottom 8 bits of the port address
                     ushort portAddress = (ushort)((AF.High << 8) | portOffset);
 
-                    _ioBus.Write(portAddress, AF.High);
+                    _simpleIoBus.WritePort(portAddress, AF.High);
 
                     return 11;
                 case 0xd5: //push bc
diff --git a/Core/Io/IO_Bus.cs b/Core/Io/IO_Bus.cs
new file mode 100644
index 0000000..b473df8
--- /dev/null
+++ b/Core/Io/IO_Bus.cs
@@ -0,0 +1,43 @@
+using System.Diagnostics;
+using Core.Interfaces;
+
+namespace Core.Io
+{
+    public class IO_Bus
+{
+    // 8 rows representing the Spectrum keyboard matrix. Default to 0xFF (unpressed).
+    public byte[] KeyboardRows = new byte[8] { 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF };
+
+    public byte ReadPort(ushort portAddress)
+    {
+        // The Spectrum ULA responds to any even port address (where the lowest bit is 0)
+        if ((portAddress & 0x01) == 0)
+        {
+            byte highByte = (byte)(portAddress >> 8); // The B register!
+            byte result = 0xFF; // Start assuming no keys are pressed
+
+            // The ROM pulls a specific bit low (0) in the high byte to request a row.
+            // Sometimes it pulls multiple bits low to scan multiple rows at once, so we AND the results.
+            if ((highByte & 0x01) == 0) result &= KeyboardRows[0]; // 0xFE: CAPS, Z, X, C, V
+            if ((highByte & 0x02) == 0) result &= KeyboardRows[1]; // 0xFD: A, S, D, F, G
+            if ((highByte & 0x04) == 0) result &= KeyboardRows[2]; // 0xFB: Q, W, E, R, T
+            if ((highByte & 0x08) == 0) result &= KeyboardRows[3]; // 0xF7: 1, 2, 3, 4, 5
+            if ((highByte & 0x10) == 0) result &= KeyboardRows[4]; // 0xEF: 0, 9, 8, 7, 6
+            if ((highByte & 0x20) == 0) result &= KeyboardRows[5]; // 0xDF: P, O, I, U, Y
+            if ((highByte & 0x40) == 0) result &= KeyboardRows[6]; // 0xBF: ENTER, L, K, J, H
+            if ((highByte & 0x80) == 0) result &= KeyboardRows[7]; // 0x7F: SPACE, SYM, M, N, B
+
+            // The top 3 bits (5, 6, 7) are unused by the keyboard and usually return 1 on a real Spectrum
+            return (byte)(result | 0xE0);
+        }
+
+        // Return 0xFF for unhandled ports
+        return 0xFF; 
+    }
+
+    public void WritePort(ushort portAddress, byte portValue)
+        {
+
+        }
+}
+}
\ No newline at end of file
diff --git a/Core/Io/SimpleIoBus.cs b/Core/Io/SimpleIoBus.cs
deleted file mode 100644
index dbb90d9..0000000
--- a/Core/Io/SimpleIoBus.cs
+++ /dev/null
@@ -1,20 +0,0 @@
-using System.Diagnostics;
-using Core.Interfaces;
-
-namespace Core.Io
-{
-    public class SimpleIoBus : IIoBus
-    {
-        public byte Read(ushort port)
-        {
-            // If the CPU reads an unconnected port, the Z80 usually sees 0xFF
-            return 0xFF;
-        }
-
-        public void Write(ushort port, byte value)
-        {
-            // For now, let's just log it to the Visual Studio Output window
-            Debug.WriteLine($"Hardware I/O Write -> Port: 0x{port:X4}, Value: 0x{value:X2}");
-        }
-    }
-}
\ No newline at end of file
diff --git a/Core/Memory/MemoryBus.cs b/Core/Memory/MemoryBus.cs
index bf1595e..43d613a 100644
--- a/Core/Memory/MemoryBus.cs
+++ b/Core/Memory/MemoryBus.cs
@@ -35,12 +35,20 @@ namespace Core.Memory
         public void CrapRAMData()
         {
             Random random = new Random();
-            for (int i = 0x4000; i < 0x5AFF; i++)
+            for (int i = 0x4000; i < 0xFFFF; i++)
             {
                 _memory[i] = (byte)random.Next(0x00, 0xFF);
             }
         }
 
+        public void CleanRAMData()
+        {            
+            for (int i = 0x4000; i < 0xFFFF; i++)
+            {
+                _memory[i] = 0x00;
+            }
+        }
+
         // Load the ROM file
         public void LoadRom(byte[] romData)
         {
diff --git a/Desktop/48.rom b/Desktop/48.rom
index 4d6895e0bbf3fa543f192a66a297192b3c969ac9..752c38ae4ed8da9e3eee9a92304741278b7ee8c5 100644
GIT binary patch
delta 41
wcmZo@U~Fh$++Zy#Wn^GvrVx-=RGgnztPqr1oSImaoT1=T@`Pb?sOV}f02QhY@Bjb+

delta 41
wcmZo@U~Fh$++Zy#WoT((q!65$mz<NBS)>q@TAZ3#l$@d9Q}SeUsOV}f02gNtNdN!<

diff --git a/Desktop/48.rom.bak b/Desktop/48.rom.bak
new file mode 100644
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GIT binary patch
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literal 0
HcmV?d00001

diff --git a/Desktop/DebuggerForm.cs b/Desktop/DebuggerForm.cs
index b15862e..07d98a1 100644
--- a/Desktop/DebuggerForm.cs
+++ b/Desktop/DebuggerForm.cs
@@ -53,7 +53,7 @@ namespace Desktop
 
         private async void btnRun_Click(object sender, EventArgs e)
         {
-            // If it is already running, this button acts as a STOP button
+            //Stops
             if (_isRunning)
             {
                 _isRunning = false;
@@ -61,7 +61,7 @@ namespace Desktop
                 return;
             }
 
-            // --- NEW: Parse the Breakpoint ---
+            //Parse the Breakpoint
             if (!string.IsNullOrWhiteSpace(txtBreakpoint.Text))
             {
                 if (ushort.TryParse(txtBreakpoint.Text, System.Globalization.NumberStyles.HexNumber, null, out ushort parsedBp))
@@ -76,18 +76,14 @@ namespace Desktop
             }
             else
             {
-                _breakpoint = null; // No text means no breakpoint
+                _breakpoint = null;
             }
-            // ---------------------------------
 
             // Start the run state
             _isRunning = true;
             btnRun.Text = "Stop";
 
-
-
-            // Fire up a background thread
-            // Fire up a background thread
+            //Background thread
             await Task.Run(() =>
             {
                 try
@@ -111,6 +107,13 @@ namespace Desktop
 
                         // --- Execute Instruction ---
                         _cpu.Step();
+                        //if (_cpu.TotalTStates % 1000 == 0)
+                        //{
+                        //    this.Invoke((MethodInvoker)delegate
+                        //    {
+                        //        UpdateDisplay();
+                        //    });
+                        //}
 
                         // --- Check for End of Frame ---
                         if (_cpu.TotalTStates >= nextFrameTargetTStates)
@@ -164,8 +167,7 @@ namespace Desktop
                 }
             });
 
-            // Whether it stopped because of a breakpoint, a crash, or the user clicking "Stop",
-            // we MUST update the UI when the background thread finishes!
+            //update the UI when the background thread finishes
             btnRun.Text = "Run";
             UpdateDisplay();
         }
diff --git a/Desktop/Form1.Designer.cs b/Desktop/Form1.Designer.cs
index ced990d..389d04b 100644
--- a/Desktop/Form1.Designer.cs
+++ b/Desktop/Form1.Designer.cs
@@ -48,6 +48,7 @@
             AutoScaleMode = AutoScaleMode.Font;
             ClientSize = new Size(791, 596);
             Controls.Add(picScreen);
+            KeyPreview = true;
             Name = "Form1";
             Text = "Parsons Sinclair ZX Spectrum 48K - 2026";
             ((System.ComponentModel.ISupportInitialize)picScreen).EndInit();
diff --git a/Desktop/Form1.cs b/Desktop/Form1.cs
index dea3f91..caa947e 100644
--- a/Desktop/Form1.cs
+++ b/Desktop/Form1.cs
@@ -13,7 +13,7 @@ namespace Desktop
     {
         private Z80 _cpu = null!;
         private MemoryBus _memoryBus = null!;
-        private SimpleIoBus _simpleIoBus = null!;
+        private IO_Bus _simpleIoBus = null!;
 
         // The 16 physical colors of the ZX Spectrum (ARGB format)
         private readonly int[] SpectrumColors = new int[]
@@ -50,7 +50,7 @@ namespace Desktop
             try
             {
                 _memoryBus = new MemoryBus();
-                _simpleIoBus = new SimpleIoBus();
+                _simpleIoBus = new IO_Bus();
 
                 _memoryBus.CrapRAMData();
                 byte[] romData = RomLoader.Load("48.rom");
@@ -120,5 +120,67 @@ namespace Desktop
             if (picScreen.Image != null) picScreen.Image.Dispose();
             picScreen.Image = bmp;
         }
+
+        // Helper method to update the IO Bus state
+        private void UpdateMatrix(int row, int col, bool isPressed)
+        {
+            if (isPressed)
+            {
+                // Clear the bit to 0 (Active-Low = Pressed)
+                _simpleIoBus.KeyboardRows[row] &= (byte)~(1 << col);
+            }
+            else
+            {
+                // Set the bit back to 1 (Unpressed)
+                _simpleIoBus.KeyboardRows[row] |= (byte)(1 << col);
+            }
+        }
+
+        // Hook this to Form1's KeyDown event
+        protected override void OnKeyDown(KeyEventArgs e)
+        {
+            HandleKey(e.KeyCode, true);
+            base.OnKeyDown(e);
+        }
+
+        // Hook this to Form1's KeyUp event
+        protected override void OnKeyUp(KeyEventArgs e)
+        {
+            HandleKey(e.KeyCode, false);
+            base.OnKeyUp(e);
+        }
+
+        private void HandleKey(Keys key, bool isPressed)
+        {
+            switch (key)
+            {
+                // Row 6: ENTER, L, K, J, H
+                case Keys.Enter: UpdateMatrix(6, 0, isPressed); break;
+                case Keys.L: UpdateMatrix(6, 1, isPressed); break;
+                case Keys.K: UpdateMatrix(6, 2, isPressed); break;
+                case Keys.J: UpdateMatrix(6, 3, isPressed); break;
+                case Keys.H: UpdateMatrix(6, 4, isPressed); break;
+
+                // Row 7: SPACE, SYM SHIFT, M, N, B
+                case Keys.Space: UpdateMatrix(7, 0, isPressed); break;
+                case Keys.M: UpdateMatrix(7, 2, isPressed); break;
+                case Keys.N: UpdateMatrix(7, 3, isPressed); break;
+                case Keys.B: UpdateMatrix(7, 4, isPressed); break;
+
+                // Row 1: A, S, D, F, G
+                case Keys.A: UpdateMatrix(1, 0, isPressed); break;
+                case Keys.S: UpdateMatrix(1, 1, isPressed); break;
+                case Keys.D: UpdateMatrix(1, 2, isPressed); break;
+                case Keys.F: UpdateMatrix(1, 3, isPressed); break;
+                case Keys.G: UpdateMatrix(1, 4, isPressed); break;
+
+                    // Map the rest of the alphabet and numbers here as you need them!
+            }
+        }
+
+        private void Form1_KeyDown(object sender, KeyEventArgs e)
+        {
+
+        }
     }
 }
\ No newline at end of file