void SN79489::WriteData(BYTE data)
{
	// if bit 7 is set the it updates the latch
	if (TestBit(data,7))
	{

		// the channel is indentified by the 6 and 5 bits
		int channel = data ;
		channel >>= 5 ;

		// turn off top bit
		channel &= 0x3 ;
		m_LatchedChannel = (CHANNEL)channel ;

		// if bit 4 is set then the channel we're latching volume, otherwise tone
		m_IsToneLatched = TestBit(data,4)?false:true ;
		
		// bottom 4 bits are the data to be updated
		BYTE channelData = data & 0xF ;

		if (m_IsToneLatched)
		{
			if (m_LatchedChannel == TONES_NOISE)
			{
				// noise register is only 4 bits, so you dont need to keep the top nibble (as there isnt one)
				m_Tones[TONES_NOISE] = channelData ;
				m_LFSR = 0x8000 ;
			}
			else
			{
				WORD currentValue = m_Tones[m_LatchedChannel] ;

				// we want to keep the top 12 bits (technically 10 bits) the same value, but replace the bottom 4
				currentValue &= 0xFFF0 ;

				// update bottom 4 bits
				currentValue |= channelData ;

				m_Tones[m_LatchedChannel] = currentValue ;
			}
		}
		else
		{
			BYTE currentValue = m_Volume[m_LatchedChannel] ;

			// we want to keep the top nibble the same
			currentValue &= 0xF0 ;

			// update bottom nibble
			currentValue |= channelData ;

			m_Volume[m_LatchedChannel] = currentValue ;
		}

	}

	// we're updating the currently latched register
	else
	{
		WORD channelData = 0;

		// the data to update with is the bottom 6 bits of the data being passed in
		channelData = data & 0x3F ;

		if (m_IsToneLatched)
		{
			if (m_LatchedChannel == TONES_NOISE)
			{
				m_Tones[TONES_NOISE] = data & 0xF ;
				m_LFSR = 0x8000 ;
			}
			else
			{
				WORD currentValue = m_Tones[m_LatchedChannel] ;
				BYTE currentLowNibble = currentValue & 0xF ;

				// update the top 6 bits (10 bit register) of the channel with the low 6 bits of the data
				channelData <<= 4 ;
				
				// we dont want to modify the low 4 bits of what was previously there
				channelData |= currentLowNibble;
				m_Tones[m_LatchedChannel] = channelData ;
			}
		}
		else
		{		
			m_Volume[m_LatchedChannel] = data & 0xF ;
		}
	}
}