Some years ago I have been using 20x4 module with 44780 controller (in fact, there were two of them). Its organization was a little bit strange, as lines order was: 0-2-1-3 (not 0-1-2-3). I can't remember exact addresses of the beginnings of each line, but it was explicit stated in the datasheet of 20x4 display module.
Zbyszek