O-Cman

[LCD]

BTW, do you know any routine that preserve the background for 1x1 sprite?

This can be done with binary OR (BOR/|) and binary AND (BAND/&) with grabbing the background, puting a mask on in in memory using AND and puting sprite data in top of it using OR, then writing it back to screen memory, but real background preservation needs to store the whole background area in memory. It will be faster in ASM.