Hi,
Even faster would be this way - but obviously the OP did not try it the way Charles described.
Not really because then the top four bits will be 0 which they might not have been when PortC was read. And IF the top four bits doesn't matter then I see no reason for not simply writing to PortC directly, ie PortC = $F which would make THIS particular example even faster....

However, I suspect that setting the low four bits to 1 are just an example. Using bitwise AND/OR could also work but I'm not sure it's faster than simply flipping the four bits in ShadowC and then writing it to the port.

/Henrik.