public void WriteScroll(byte data)
{
if (!WriteLatch) // First write.
{
// The data is split into two parts. The first 3 bits are the fine X scroll and the upper 5 bits are
// the course X scroll.
FineX = (byte)(data & 0b000_0111);
// Set course X in the temporary address register without touching the other
TAddress = (ushort)((TAddress & ~0x001f) | ((data >> 3) & 0x001f));
WriteLatch = true;
}
else // Second write.
{
// The data is split into two parts again. The first 5 bits are the course Y scroll and the upper 3
// bits are the fine Y scroll.
// First set the course Y scroll in the temporary address register without touching the other
// Course Y is stored as bits 3-7 in data so we only have to left shift data by 2 to get bits 3-7 into
// positions 5-9 for the temporary address register.
TAddress = (ushort)((TAddress & ~0x03e0) | ((data << 2) & 0x03e0));
// Now set the fine Y scroll in the temporary address register without touching the other Fine Y
// is stored as bits 0-2 in data so we have to left shift data by 12 to get bits 0-2 into positions
// 12-14.
TAddress = (ushort)((TAddress & ~0x7000) | ((data << 12) & 0x7000));
WriteLatch = false;
}
}
public void WriteAddress(byte data)
{
if (!WriteLatch) // First write.
{
// Write data into the high byte position of the temporary address register. Don't touch the low byte
// of the temporary address register.
TAddress = (ushort)((TAddress & ~0xff00) | ((data << 8) & 0xff00));
// We do have to set bit 15 of the temporary address register to zero since it technically doesn't
// exist.
TAddress &= 0x7fff; // Mask the bottom 15
WriteLatch = true;
}
else // Second write.
{
// Write data into the low byte position of the temporary address register. Don't touch the high byte
// of the temporary address register.
TAddress = (TAddress & ~0x00ff) | data;
// Set the current address register to the value of the temporary address register.
VAddress = TAddress;
WriteLatch = false;
}
}
