public void BIT(OpcodeContainer container, ushort address)
{
var value = CPU.ReadByteAt(address);
CPU.IsOverflowed = (value & 0x40) != 0;
CPU.IsNegative = (value & 0x80) != 0;
CPU.IsZero = (value & CPU.Registers.A) == 0;
}
public static ushort GetIndirectX(MOS6502 CPU)
{
var incompleteXAddress = CPU.ReadNextByte();
CPU.IncrementPC();
var intermediateAddress = (byte)(incompleteXAddress + CPU.Registers.X);
return(intermediateAddress == 0xFF
? (ushort)(CPU.ReadByteAt(0xFF) | CPU.ReadByteAt(0x00) << 8)
: CPU.ReadShortAt(intermediateAddress));
}
public static ushort GetIndirectYWrite(MOS6502 CPU)
{
intermediateAddress = CPU.ReadNextByte();
CPU.IncrementPC();
var baseAddress = intermediateAddress == 0xFF
? (ushort)(CPU.ReadByteAt(0xFF) | CPU.ReadByteAt(0x00) << 8)
: CPU.ReadShortAt((ushort)intermediateAddress);
CPU.CycleFinished();
return((ushort)(baseAddress + CPU.Registers.Y));
}
public static ushort GetIndirect(MOS6502 CPU)
{
intermediateAddress = CPU.ReadNextShort();
// 6502 bug in indirect JMP...
if ((intermediateAddress & 0x00FF) == 0xFF)
{
byte lowByte = CPU.ReadByteAt(intermediateAddress);
byte highByte = CPU.ReadByteAt((ushort)(intermediateAddress - 0x00FF));
return((ushort)(highByte << 8 | lowByte));
}
return(CPU.ReadShortAt(intermediateAddress));
}
public static ushort GetIndirectY(MOS6502 CPU)
{
intermediateAddress = CPU.ReadNextByte();
CPU.IncrementPC();
var baseAddress = intermediateAddress == 0xFF
? (ushort)(CPU.ReadByteAt(0xFF) | CPU.ReadByteAt(0x00) << 8)
: CPU.ReadShortAt((ushort)intermediateAddress);
var finalAddress = (ushort)(baseAddress + CPU.Registers.Y);
if (AddressingMode.NotSamePage(baseAddress, CPU.Registers.Y))
{
CPU.CycleFinished();
}
return(finalAddress);
}