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Implemented a load more Z80 OpCodes

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This commit is contained in:
Marc Parsons
2026-04-13 18:00:19 +01:00
parent ed0772f27a
commit c642f7a6c6
2 changed files with 63 additions and 3 deletions
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34
Core/Cpu/Z80.cs
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@@ -322,6 +322,9 @@ namespace Core.Cpu
case 0x04: // INC B
BC.High = Inc8(BC.High);
return 4;
case 0x0E: // LD C, n
BC.Low = FetchByte();
return 7; // Takes 7 T-States
case 0x10: // DJNZ d
sbyte djnzOffset = (sbyte)FetchByte();
@@ -606,7 +609,7 @@ namespace Core.Cpu
targetAddress = (ushort)(IY.Word + offset75);
// Write the low byte of HL to memory
_memory.Write(targetAddress, HL.Low);
return 19;
return 19;
case 0xCB: // The FD CB nested prefix
{
sbyte offsetCB = (sbyte)FetchByte(); // This is the '01'
@@ -615,6 +618,35 @@ namespace Core.Cpu
switch (bitOpcode)
{
case 0x4E: // BIT 1, (IY+d)
{
byte memValBit = _memory.Read(targetAddress);
// Check if bit 1 is 0
bool bitIsZero = (memValBit & 0x02) == 0;
// Preserve the Carry flag (Bit 0), clear everything else
AF.Low &= 0x01;
// Set Half-Carry (Bit 4) - Standard Z80 behavior for BIT
AF.Low |= 0x10;
if (bitIsZero)
{
AF.Low |= 0x40; // Set Zero Flag (Bit 6)
AF.Low |= 0x04; // Set P/V Flag (Bit 2)
}
return 20; // Takes 20 T-States
}
case 0x8E: // RES 1, (IY+d)
byte memValRes = _memory.Read(targetAddress);
// 0xFD is Binary 1111 1101.
// ANDing with this preserves all bits except Bit 1, which becomes 0.
memValRes &= 0xFD;
_memory.Write(targetAddress, memValRes);
return 23;
case 0xCE: // SET 1, (IY+d)
memVal = _memory.Read(targetAddress);
memVal |= 0x02; // 0x02 is Binary 0000 0010 (Bit 1)

32
Desktop/DebuggerForm.cs
View File

@@ -235,6 +235,11 @@ namespace Desktop
case 0x04:
mnemonic = "INC B";
break;
case 0x0E:
byte cImm = _memoryBus.Read((ushort)(currentPc + 1));
mnemonic = $"LD C, 0x{cImm:X2}";
instructionLength = 2;
break;
case 0x10:
sbyte djnzOffset = (sbyte)_memoryBus.Read((ushort)(currentPc + 1));
ushort djnzDest = (ushort)(currentPc + 2 + djnzOffset);
@@ -435,8 +440,11 @@ namespace Desktop
sbyte d = (sbyte)_memoryBus.Read((ushort)(currentPc + 2));
byte cbOpcode = _memoryBus.Read((ushort)(currentPc + 3));
string sign = d >= 0 ? "+" : "";
if (cbOpcode == 0xCE)
if (cbOpcode == 0x4E)
{
mnemonic = $"BIT 1, (IY{sign}{d})";
}
else if (cbOpcode == 0xCE)
{
mnemonic = $"SET 1, (IY{sign}{d})";
}
@@ -453,6 +461,26 @@ namespace Desktop
mnemonic = $"LD (IY{sign}{d}), L";
instructionLength = 3;
}
else if (fdOpcode == 0xCB) // FD CB prefix
{
sbyte d = (sbyte)_memoryBus.Read((ushort)(currentPc + 2));
byte cbOpcode = _memoryBus.Read((ushort)(currentPc + 3));
string sign = d >= 0 ? "+" : "";
if (cbOpcode == 0xCE)
{
mnemonic = $"SET 1, (IY{sign}{d})";
}
else if (cbOpcode == 0x8E)
{
mnemonic = $"RES 1, (IY{sign}{d})";
}
else
{
mnemonic = $"FD CB {d:X2} {cbOpcode:X2}"; // Fallback
}
instructionLength = 4;
}
else
{
mnemonic = $"FD PREFIX UNKNOWN (0x{fdOpcode:X2})";