Advice on a style issue(writing funcions)

I once read an author that suggestion that one shouldnt write a function (or module) that took more then a screen(would be nice to know what resolution and letter size he meant :)) .. Now I usually write functions that take more than a screen, perhaps two or two and half and in myh opinion there is no convenient way of splitting it up or giving parts of it to another subfunction or subroutine.. Any advices for this style issue ?