public override void Execute(CPUState state, Bus bus)
{
if (state.HasStatusFlag(StatusFlag.Zero))
{
state.PC = (ushort)CalculateEffectiveAddress(state, bus);
}
}
public override void Execute(CPUState state, Bus bus)
{
byte operandValue = GetOperandValue(state, bus);
int result = state.Accumulator + operandValue + (state.HasStatusFlag(StatusFlag.Carry) ? 1 : 0);
CheckOverflowFlag(state, state.Accumulator, operandValue, result);
// Need to work here with integer result as we need to look at the 9th bit for carry
state.ChangeStatusFlag(StatusFlag.Carry, (result & 0x100) != 0);
state.Accumulator = (byte)result;
CheckNegativeFlag(state, state.Accumulator);
CheckZeroFlag(state, state.Accumulator);
}
public override void Execute(CPUState state, Bus bus)
{
// Same as ADC, just used one's complement of the operand
byte operandValue = (byte)~GetOperandValue(state, bus);
int result = state.Accumulator + operandValue + (state.HasStatusFlag(StatusFlag.Carry) ? 1 : 0);
// TODO: learn how this works: http://www.righto.com/2012/12/the-6502-overflow-flag-explained.html
CheckOverflowFlag(state, state.Accumulator, operandValue, result);
// Need to work here with integer result as we need to look at the 9th bit for carry
state.ChangeStatusFlag(StatusFlag.Carry, (result & 0x100) != 0);
state.Accumulator = (byte)result;
CheckNegativeFlag(state, state.Accumulator);
CheckZeroFlag(state, state.Accumulator);
}
public override void Execute(CPUState state, Bus bus)
{
byte result;
int carryBitmask = state.HasStatusFlag(StatusFlag.Carry) ? 0x80 : 0;
if (Instruction.AddressMode != AddressMode.Accumulator)
{
int effectiveAddress = CalculateEffectiveAddress(state, bus);
byte operandValue = bus.Read(effectiveAddress);
state.ChangeStatusFlag(StatusFlag.Carry, (operandValue & 1) == 1); // The lowest bit is displaced by the left shift and stored as a carry flag
result = (byte)((operandValue >> 1) | carryBitmask); // Set the carry bit in the shifted value via bitwise OR
bus.Write(effectiveAddress, result);
}
else
{
state.ChangeStatusFlag(StatusFlag.Carry, (state.Accumulator & 1) == 1); // The lowest bit is displaced by the left shift and stored as a carry flag
result = (byte)((state.Accumulator >> 1) | carryBitmask); // Set the carry bit in the shifted value via bitwise OR
state.Accumulator = result;
}
CheckZeroFlag(state, result);
CheckNegativeFlag(state, result);
}
