I need to output a byte to LPT port. For this there's an option to program I/O ports directly (with ioperm & outb), but only if LPT port is a standard PC one (ports 0x378, 0x278, etc.). But i need a 'portable' way of doing this, i.e. which would also work on such interfaces as USB2LPT. I guess these adaptors will also have /dev/lp[0-9]* interface (am i right?). Here's what i get currently:

$ echo 1 > /dev/lp0
^C

I.e. i have to use Ctrl+C because 'echo' never exits. When i had a printer connected to LPT, this did work.

So, how can i output some data in portable way, without I/O ports programming and hangs described above?

I believe the reason for it hanging is that parallel ports require a port pulled low or high like serial DTR pins

There are several control signals at the parallel port. They control whether there are errors, the printer is out of paper, is ready, ... By default the parallel port driver waits for the printer to be ready and thus waits forever. You can set several parameters with the tunelp command.

How about:
Where "lp" is the system default printer configured in CUPS.

Default printer is configured on USB port. Anyway, there might be no LPT printers configured in CUPS, but i still would need to have things work.

Thanks, i'll try this.