I am Planning to build a parallel port led dimmer using ti's TLC5904 which uses 8 data inputs for adjusting the brightness or in other words current . you can control upto 15 LED's using this IC . I know how to interface the parallel port But there is some complication in this is , i don't understand what is a DOUT For , DIN DCLK are used for input for brighness control , and there input will come from a parallel port , since a parallel port is a 8 bit ouput from a computer . i don't know why dclk is for , do i have give external clock pulse . here is the ic pinout tlc5904.pdf