I am using a laptop ( windows 7 and 64 bit) I bought usb to parallel connector as i want to control the LED's through the data lines of the parallel pin( 25 pins)... So i am trying indirectly to use a LPT port.. please tell me how to go about.. The code works fine on desktop PC when connected to parallel port..
I have never seen a gadget that claims to be a real usb-to-parallel converter. I have seen usb-to-printer-port converters, but they do just that: create a windows virtual printer port.
The difference between usb-to-printer converters and usb-to-serial converters is not so much the converter itself, but the (sad) fact that windows software often seems to use the windows serial port interface, so a usb-to-serial converter can sneak beneath that interface and preent itself to the unnkowing program as a serial port.
AFAIK there is no compareable windows parallel port interface, so windows programs use either the windows printer interface (which is at the level of print this file using this printer driver) or use the parallel port hardware directly. It is probably not totally impossible to emulate the parallel port in hardware, but I have not seen a product that does so. (but check AndrejanKo's comment)
So for the hardware hacker an usb-to-serial converter can be almost as usefull as a real serial port, but an usb-to-parallel converter (which should be called usb-to-printer converter) is almost useless.
Something like an FT245 is effectively a USB to parallel converter - as distinct from the commodity USB-to-printer converters sold at computer shops.
One could also build similar functionality using an USB enabled microcontroller which can have its program customized.
However, as the USB bus is packetized and has a fair amount of latency, it is a poor way to do "bit bang" type manipulations. When such are needed, it is better to move the "bit bang" logic to the USB microcontroller, and have the PC send higher level commands instead - getting back towards what the commodity printer adapters are an application-specific example of.
You might want to hunt recycling facilities for an old PC with an actual localbus printer port...