From the datasheet I have seen (link below) this 4x40 LDC has only one enable pin.(This is the only 4x40 that I have seen)

http://www.futurlec.com/LED/LCD40X4BL.shtml


Black square most of the times appear when you have a wrong contrast setting

(you should have a pot with the center tap connected to pin 3 to adjust the contrast)

Al.