Implemented many more OpCodes

Core/Cpu/Z80.cs

@@ -50,13 +50,33 @@ namespace Core.Cpu
         public void Reset()
         {
             PC = 0x0000;
-            // The Z80 initializes SP to 0xFFFF on boot
+            SP = 0xFFFF; // The Z80 initializes SP to 0xFFFF on boot
-            SP = 0xFFFF;
 
+            // Main Registers
             AF.Word = 0;
             BC.Word = 0;
             DE.Word = 0;
             HL.Word = 0;
+
+            // Alternate Registers
+            AF_Prime.Word = 0;
+            BC_Prime.Word = 0;
+            DE_Prime.Word = 0;
+            HL_Prime.Word = 0;
+
+            // Index Registers
+            IX.Word = 0;
+            IY.Word = 0;
+
+            // Internal Registers
+            I = 0;
+            R = 0;
+
+            // Hardware State
+            IFF1 = false;
+            IFF2 = false;
+            InterruptMode = 0;
+            TotalTStates = 0; // Reset the system clock!
         }
 
         public int Step()
@@ -96,6 +116,36 @@ namespace Core.Cpu
                    $"C:{f & 1}";
         }
 
+        private void Sub(byte value)
+        {
+            byte a = AF.High;
+            int result = a - value;
+
+            // Save the result back to the Accumulator
+            AF.High = (byte)result;
+
+            // --- Update Flags (F Register) ---
+            AF.Low = 0; // Clear all flags
+
+            // Sign Flag (Bit 7)
+            if ((result & 0x80) != 0) AF.Low |= 0x80;
+
+            // Zero Flag (Bit 6)
+            if ((byte)result == 0) AF.Low |= 0x40;
+
+            // Half-Carry Flag (Bit 4) - Set if borrow from bit 4
+            if (((a & 0x0F) - (value & 0x0F)) < 0) AF.Low |= 0x10;
+
+            // Overflow Flag (Bit 2) - Set if operands have different signs and result sign changes
+            if ((((a ^ value) & 0x80) != 0) && (((a ^ result) & 0x80) != 0)) AF.Low |= 0x04;
+
+            // Subtract Flag (Bit 1) - ALWAYS set for CP/SUB
+            AF.Low |= 0x02;
+
+            // Carry Flag (Bit 0) - Set if the overall result dropped below 0
+            if (result < 0) AF.Low |= 0x01;
+        }
+
         private void Sbc(byte value)
         {
             byte a = AF.High;
@@ -309,6 +359,17 @@ namespace Core.Cpu
             _memory.Write(SP, (byte)(value & 0xFF));
         }
 
+        private ushort Pop()
+        {
+            // The Z80 is Little-Endian. Low byte comes off the stack first.
+            byte low = _memory.Read(SP++);
+
+            // High byte comes off second.
+            byte high = _memory.Read(SP++);
+
+            return (ushort)((high << 8) | low);
+        }
+
         private int ExecuteOpcode(byte opcode)
         {
             sbyte offset = 0;
@@ -340,6 +401,9 @@ namespace Core.Cpu
                 case 0x11: //LD DE, nn
                     DE.Word = FetchWord();
                     return 10;
+                case 0x16: // LD D, n
+                    DE.High = FetchByte();
+                    return 7;
                 case 0x19: // ADD HL, DE
                     Add16(DE.Word);
                     return 11; 
@@ -429,9 +493,15 @@ namespace Core.Cpu
                 case 0x77: // LD (HL), A
                     _memory.Write(HL.Word, AF.High);
                     return 7;
+                case 0x91: // SUB C
+                    Sub(BC.Low);
+                    return 4; // Takes 4 T-States
                 case 0xA7: // AND A
                     And(AF.High);
                     return 4;
+                case 0x5F: // LD E, A
+                    DE.Low = AF.High;
+                    return 4;
                 case 0xAF: // XOR A
                     AF.High = 0;
                     AF.Low = 0x44;
@@ -442,6 +512,9 @@ namespace Core.Cpu
                 case 0xC3:
                     PC = FetchWord();
                     return 10;
+                case 0xC9: // RET
+                    PC = Pop();
+                    return 10;
                 case 0xCD: // CALL nn
                     ushort callAddress = FetchWord();
                     Push(PC);
@@ -604,6 +677,24 @@ namespace Core.Cpu
                     byte decVal = Dec8(memVal);
                     _memory.Write(targetAddress, decVal);
                     return 23;
+                case 0x36: // LD (IY+d), n
+                    {
+                        sbyte offset36 = (sbyte)FetchByte();
+                        byte nValue = FetchByte();
+                        targetAddress = (ushort)(IY.Word + offset36);
+
+                        _memory.Write(targetAddress, nValue);
+                        return 19; // Takes 19 T-States
+                    }
+                case 0x71: // LD (IY+d), C
+                    {
+                        sbyte offset71 = (sbyte)FetchByte();
+                        targetAddress = (ushort)(IY.Word + offset71);
+
+                        // Write the C register (low byte of BC) to memory
+                        _memory.Write(targetAddress, BC.Low);
+                        return 19; // Takes 19 T-States
+                    }
                 case 0x75: // LD (IY+d), L                    
                         sbyte offset75 = (sbyte)FetchByte();
                         targetAddress = (ushort)(IY.Word + offset75);

Core/Memory/MemoryBus.cs

@@ -42,5 +42,10 @@ namespace Core.Memory
             // Copy the ROM
             Array.Copy(romData, 0, _memory, 0, romData.Length);
         }
+
+        public void ClearRam()
+        {
+            //To Do
+        }
     }
 }

Desktop/DebuggerForm.Designer.cs

@@ -53,94 +53,95 @@
             lblIff1 = new Label();
             lblIff2 = new Label();
             lblIE = new Label();
+            btnReset = new Button();
             SuspendLayout();
             // 
             // lblAF
             // 
             lblAF.AutoSize = true;
-            lblAF.Location = new Point(10, 7);
+            lblAF.Location = new Point(12, 9);
             lblAF.Margin = new Padding(2, 0, 2, 0);
             lblAF.Name = "lblAF";
-            lblAF.Size = new Size(26, 20);
+            lblAF.Size = new Size(33, 25);
             lblAF.TabIndex = 0;
             lblAF.Text = "AF";
             // 
             // lblBC
             // 
             lblBC.AutoSize = true;
-            lblBC.Location = new Point(9, 48);
+            lblBC.Location = new Point(11, 60);
             lblBC.Margin = new Padding(2, 0, 2, 0);
             lblBC.Name = "lblBC";
-            lblBC.Size = new Size(27, 20);
+            lblBC.Size = new Size(33, 25);
             lblBC.TabIndex = 1;
             lblBC.Text = "BC";
             // 
             // lblDE
             // 
             lblDE.AutoSize = true;
-            lblDE.Location = new Point(10, 100);
+            lblDE.Location = new Point(12, 125);
             lblDE.Margin = new Padding(2, 0, 2, 0);
             lblDE.Name = "lblDE";
-            lblDE.Size = new Size(28, 20);
+            lblDE.Size = new Size(34, 25);
             lblDE.TabIndex = 2;
             lblDE.Text = "DE";
             // 
             // lblHL
             // 
             lblHL.AutoSize = true;
-            lblHL.Location = new Point(10, 150);
+            lblHL.Location = new Point(12, 188);
             lblHL.Margin = new Padding(2, 0, 2, 0);
             lblHL.Name = "lblHL";
-            lblHL.Size = new Size(27, 20);
+            lblHL.Size = new Size(33, 25);
             lblHL.TabIndex = 3;
             lblHL.Text = "HL";
             // 
             // lblPC
             // 
             lblPC.AutoSize = true;
-            lblPC.Location = new Point(9, 200);
+            lblPC.Location = new Point(11, 250);
             lblPC.Margin = new Padding(2, 0, 2, 0);
             lblPC.Name = "lblPC";
-            lblPC.Size = new Size(26, 20);
+            lblPC.Size = new Size(33, 25);
             lblPC.TabIndex = 4;
             lblPC.Text = "PC";
             // 
             // lblSP
             // 
             lblSP.AutoSize = true;
-            lblSP.Location = new Point(9, 252);
+            lblSP.Location = new Point(11, 315);
             lblSP.Margin = new Padding(2, 0, 2, 0);
             lblSP.Name = "lblSP";
-            lblSP.Size = new Size(25, 20);
+            lblSP.Size = new Size(32, 25);
             lblSP.TabIndex = 6;
             lblSP.Text = "SP";
             // 
             // lblFlags
             // 
             lblFlags.AutoSize = true;
-            lblFlags.Location = new Point(88, 52);
+            lblFlags.Location = new Point(110, 65);
             lblFlags.Margin = new Padding(2, 0, 2, 0);
             lblFlags.Name = "lblFlags";
-            lblFlags.Size = new Size(43, 20);
+            lblFlags.Size = new Size(53, 25);
             lblFlags.TabIndex = 7;
             lblFlags.Text = "Flags";
             // 
             // lblTStates
             // 
             lblTStates.AutoSize = true;
-            lblTStates.Location = new Point(88, 7);
+            lblTStates.Location = new Point(110, 9);
             lblTStates.Margin = new Padding(2, 0, 2, 0);
             lblTStates.Name = "lblTStates";
-            lblTStates.Size = new Size(63, 20);
+            lblTStates.Size = new Size(75, 25);
             lblTStates.TabIndex = 8;
             lblTStates.Text = "T-States";
             // 
             // txtMemoryStart
             // 
-            txtMemoryStart.Location = new Point(300, 21);
+            txtMemoryStart.Location = new Point(375, 26);
             txtMemoryStart.Margin = new Padding(2);
             txtMemoryStart.Name = "txtMemoryStart";
-            txtMemoryStart.Size = new Size(121, 27);
+            txtMemoryStart.Size = new Size(150, 31);
             txtMemoryStart.TabIndex = 9;
             txtMemoryStart.Text = "Memory Start";
             txtMemoryStart.TextAlign = HorizontalAlignment.Center;
@@ -148,10 +149,10 @@
             // 
             // btnStep
             // 
-            btnStep.Location = new Point(6, 418);
+            btnStep.Location = new Point(8, 522);
             btnStep.Margin = new Padding(2);
             btnStep.Name = "btnStep";
-            btnStep.Size = new Size(90, 27);
+            btnStep.Size = new Size(112, 34);
             btnStep.TabIndex = 12;
             btnStep.Text = "Step";
             btnStep.UseVisualStyleBackColor = true;
@@ -159,10 +160,10 @@
             // 
             // btnRun
             // 
-            btnRun.Location = new Point(119, 418);
+            btnRun.Location = new Point(149, 522);
             btnRun.Margin = new Padding(2);
             btnRun.Name = "btnRun";
-            btnRun.Size = new Size(90, 27);
+            btnRun.Size = new Size(112, 34);
             btnRun.TabIndex = 13;
             btnRun.Text = "Run";
             btnRun.UseVisualStyleBackColor = true;
@@ -170,10 +171,10 @@
             // 
             // btnRefreshMemory
             // 
-            btnRefreshMemory.Location = new Point(425, 21);
+            btnRefreshMemory.Location = new Point(531, 26);
             btnRefreshMemory.Margin = new Padding(2);
             btnRefreshMemory.Name = "btnRefreshMemory";
-            btnRefreshMemory.Size = new Size(90, 27);
+            btnRefreshMemory.Size = new Size(112, 34);
             btnRefreshMemory.TabIndex = 14;
             btnRefreshMemory.Text = "Refresh Memory";
             btnRefreshMemory.UseVisualStyleBackColor = true;
@@ -181,37 +182,39 @@
             // 
             // txtMemoryView
             // 
-            txtMemoryView.Location = new Point(88, 80);
+            txtMemoryView.Location = new Point(110, 100);
             txtMemoryView.Margin = new Padding(2);
             txtMemoryView.Name = "txtMemoryView";
-            txtMemoryView.Size = new Size(416, 195);
+            txtMemoryView.Size = new Size(519, 243);
             txtMemoryView.TabIndex = 15;
             txtMemoryView.Text = "Memory View Window";
             // 
             // lstDisassembly
             // 
             lstDisassembly.FormattingEnabled = true;
-            lstDisassembly.Location = new Point(523, 11);
+            lstDisassembly.ItemHeight = 25;
+            lstDisassembly.Location = new Point(654, 14);
             lstDisassembly.Margin = new Padding(2);
             lstDisassembly.Name = "lstDisassembly";
-            lstDisassembly.Size = new Size(252, 264);
+            lstDisassembly.Size = new Size(314, 329);
             lstDisassembly.TabIndex = 16;
             // 
             // lstStack
             // 
             lstStack.FormattingEnabled = true;
-            lstStack.Location = new Point(779, 11);
+            lstStack.ItemHeight = 25;
+            lstStack.Location = new Point(974, 14);
             lstStack.Margin = new Padding(2);
             lstStack.Name = "lstStack";
-            lstStack.Size = new Size(130, 264);
+            lstStack.Size = new Size(162, 329);
             lstStack.TabIndex = 17;
             // 
             // btnExit
             // 
-            btnExit.Location = new Point(815, 416);
+            btnExit.Location = new Point(1019, 520);
             btnExit.Margin = new Padding(2);
             btnExit.Name = "btnExit";
-            btnExit.Size = new Size(90, 27);
+            btnExit.Size = new Size(112, 34);
             btnExit.TabIndex = 18;
             btnExit.Text = "Full Exit";
             btnExit.UseVisualStyleBackColor = true;
@@ -220,80 +223,97 @@
             // label1
             // 
             label1.AutoSize = true;
-            label1.Location = new Point(200, 278);
+            label1.Location = new Point(250, 348);
+            label1.Margin = new Padding(4, 0, 4, 0);
             label1.Name = "label1";
-            label1.Size = new Size(81, 20);
+            label1.Size = new Size(97, 25);
             label1.TabIndex = 19;
             label1.Text = "Breakpoint";
             // 
             // txtBreakpoint
             // 
-            txtBreakpoint.Location = new Point(376, 281);
+            txtBreakpoint.Location = new Point(470, 351);
+            txtBreakpoint.Margin = new Padding(4);
             txtBreakpoint.Name = "txtBreakpoint";
-            txtBreakpoint.Size = new Size(125, 27);
+            txtBreakpoint.Size = new Size(155, 31);
             txtBreakpoint.TabIndex = 20;
             // 
             // label2
             // 
             label2.AutoSize = true;
-            label2.Location = new Point(233, 21);
+            label2.Location = new Point(291, 26);
+            label2.Margin = new Padding(4, 0, 4, 0);
             label2.Name = "label2";
-            label2.Size = new Size(62, 20);
+            label2.Size = new Size(77, 25);
             label2.TabIndex = 21;
             label2.Text = "Address";
             // 
             // lblIX
             // 
             lblIX.AutoSize = true;
-            lblIX.Location = new Point(9, 298);
+            lblIX.Location = new Point(11, 372);
             lblIX.Margin = new Padding(2, 0, 2, 0);
             lblIX.Name = "lblIX";
-            lblIX.Size = new Size(22, 20);
+            lblIX.Size = new Size(28, 25);
             lblIX.TabIndex = 22;
             lblIX.Text = "IX";
             // 
             // lblIY
             // 
             lblIY.AutoSize = true;
-            lblIY.Location = new Point(10, 344);
+            lblIY.Location = new Point(12, 430);
             lblIY.Margin = new Padding(2, 0, 2, 0);
             lblIY.Name = "lblIY";
-            lblIY.Size = new Size(21, 20);
+            lblIY.Size = new Size(27, 25);
             lblIY.TabIndex = 23;
             lblIY.Text = "IY";
             // 
             // lblIff1
             // 
             lblIff1.AutoSize = true;
-            lblIff1.Location = new Point(88, 298);
+            lblIff1.Location = new Point(110, 372);
+            lblIff1.Margin = new Padding(4, 0, 4, 0);
             lblIff1.Name = "lblIff1";
-            lblIff1.Size = new Size(35, 20);
+            lblIff1.Size = new Size(45, 25);
             lblIff1.TabIndex = 24;
             lblIff1.Text = "IFF1";
             // 
             // lblIff2
             // 
             lblIff2.AutoSize = true;
-            lblIff2.Location = new Point(88, 345);
+            lblIff2.Location = new Point(110, 431);
+            lblIff2.Margin = new Padding(4, 0, 4, 0);
             lblIff2.Name = "lblIff2";
-            lblIff2.Size = new Size(35, 20);
+            lblIff2.Size = new Size(45, 25);
             lblIff2.TabIndex = 25;
             lblIff2.Text = "IFF2";
             // 
             // lblIE
             // 
             lblIE.AutoSize = true;
-            lblIE.Location = new Point(200, 345);
+            lblIE.Location = new Point(250, 431);
+            lblIE.Margin = new Padding(4, 0, 4, 0);
             lblIE.Name = "lblIE";
-            lblIE.Size = new Size(109, 20);
+            lblIE.Size = new Size(133, 25);
             lblIE.TabIndex = 26;
             lblIE.Text = "Interrupt Mode";
             // 
+            // btnReset
+            // 
+            btnReset.Location = new Point(883, 520);
+            btnReset.Name = "btnReset";
+            btnReset.Size = new Size(112, 34);
+            btnReset.TabIndex = 27;
+            btnReset.Text = "Hard Reset";
+            btnReset.UseVisualStyleBackColor = true;
+            btnReset.Click += btnReset_Click;
+            // 
             // DebuggerForm
             // 
-            AutoScaleDimensions = new SizeF(8F, 20F);
+            AutoScaleDimensions = new SizeF(10F, 25F);
             AutoScaleMode = AutoScaleMode.Font;
-            ClientSize = new Size(928, 454);
+            ClientSize = new Size(1160, 568);
+            Controls.Add(btnReset);
             Controls.Add(lblIE);
             Controls.Add(lblIff2);
             Controls.Add(lblIff1);
@@ -352,6 +372,7 @@
         private Label lblIff1;
         private Label lblIff2;
         private Label lblIE;
+        private Button btnReset;
         //private TextBox textBox4;
     }
 }

Desktop/DebuggerForm.cs

@@ -117,6 +117,30 @@ namespace Desktop
             UpdateDisplay();
         }
 
+        private void btnReset_Click(object sender, EventArgs e)
+        {
+            // 1. Safely stop the emulator if it is currently in a Run loop
+            if (_isRunning)
+            {
+                _isRunning = false;
+                btnRun.Text = "Run";
+            }
+
+            // 2. Power cycle the CPU
+            _cpu.Reset();
+
+            // Note: A true hard reset also wipes the RAM. 
+            // If you add a RAM clear method to your MemoryBus later, call it here!
+            _memoryBus.ClearRam(); //To Do
+
+            // 3. Clear the UI tracking lists
+            lstDisassembly.Items.Clear();
+            lstStack.Items.Clear();
+
+            // 4. Force a full UI refresh to show the clean slate
+            UpdateDisplay();
+        }
+
         private void btnExit_Click(object sender, EventArgs e)
         {
             Environment.Exit(0);
@@ -253,6 +277,11 @@ namespace Desktop
                         mnemonic = $"LD DE, 0x{deHigh:X2}{deLow:X2}";
                         instructionLength = 3;
                         break;
+                    case 0x16:
+                        byte dImm = _memoryBus.Read((ushort)(currentPc + 1));
+                        mnemonic = $"LD D, 0x{dImm:X2}";
+                        instructionLength = 2;
+                        break;
                     case 0x19:
                         mnemonic = "ADD HL, DE";
                         break;
@@ -321,6 +350,9 @@ namespace Desktop
                     case 0x47:
                         mnemonic = "LD B, A";
                         break;
+                    case 0x5F:
+                        mnemonic = "LD E, A";
+                        break;
                     case 0x62:
                         mnemonic = "LD H, D";
                         break;
@@ -330,6 +362,9 @@ namespace Desktop
                     case 0x77:
                         mnemonic = "LD (HL), A";
                         break;
+                    case 0x91:
+                        mnemonic = "SUB C";
+                        break;
                     case 0xA7:
                         mnemonic = "AND A";
                         break;
@@ -346,6 +381,9 @@ namespace Desktop
                         mnemonic = $"JP 0x{jpHigh:X2}{jpLow:X2}";
                         instructionLength = 3;
                         break;
+                    case 0xC9:
+                        mnemonic = "RET";
+                        break;
                     case 0xCD:
                             ushort callDest = (ushort)(_memoryBus.Read((ushort)(currentPc + 1)) | (_memoryBus.Read((ushort)(currentPc + 2)) << 8));
                             mnemonic = $"CALL 0x{callDest:X4}";
@@ -435,6 +473,14 @@ namespace Desktop
                                 mnemonic = $"DEC (IY{sign}{d})";
                                 instructionLength = 3;
                             }
+                            else if (fdOpcode == 0x36) // LD (IY+d), n
+                            {
+                                sbyte d = (sbyte)_memoryBus.Read((ushort)(currentPc + 2));
+                                byte n = _memoryBus.Read((ushort)(currentPc + 3));
+                                string sign = d >= 0 ? "+" : "";
+                                mnemonic = $"LD (IY{sign}{d}), 0x{n:X2}";
+                                instructionLength = 4;
+                            }
                             else if (fdOpcode == 0xCB) // FD CB prefix
                             {
                                 sbyte d = (sbyte)_memoryBus.Read((ushort)(currentPc + 2));
@@ -454,6 +500,13 @@ namespace Desktop
                                 }
                                 instructionLength = 4;
                             }
+                            else if (fdOpcode == 0x71) // LD (IY+d), C
+                            {
+                                sbyte d = (sbyte)_memoryBus.Read((ushort)(currentPc + 2));
+                                string sign = d >= 0 ? "+" : "";
+                                mnemonic = $"LD (IY{sign}{d}), C";
+                                instructionLength = 3;
+                            }
                             else if (fdOpcode == 0x75) // LD (IY+d), L
                             {
                                 sbyte d = (sbyte)_memoryBus.Read((ushort)(currentPc + 2));