i am using 2 line lcd display module . the module uses hd44780 driver. while my programme works for first line , the second line does'nt get activated. the driver manual says to use 40h as ddram address for second line. i went by the above instruction but without sucess. to check if my programming is correct i programmed the first line to have dispaly in the first and fifth position by changing the address counter as given in the manual . it worked properly. can anyone suggest what could be the problem

What font are you using? 44780's allow the use of 2 fonts, 5*7 and 5*10 pixels. If you selected 5*10 pixels then the 2nd row is unavailable.

most probably you didn't initiliaze it properly
there is a command to select display for 1 line, or 2 lines
check the lcd datasheet properly