PC parallel port, input

I've used the PC parallel port in several projects in order to provide
output digital signals to an external circuit (the parallel port outputs
are TTL buffered, and can source max 2 mA and sink considerably more).

Anyway, now I'm trying to find specs on how to properly use the parallel
port's level-active input lines - the Status bits (Busy, PaperEnd,
SelectIn, Error). But I can't find much in the way of specifications for
how the inputs work. Are these pure TTL as well?

Since I don't have my own +5 supply on the external circuit, would it be
safe to set one of the parallell port's output bits high and use that as a
+5v source? e.g.

----------
PC gnd ----------------|\\ |
| | Q1 |
Error (inp) -------|---|-/ |
\ | --|
22k / | LED /\ |
\ | -- |
D0 (out) / | --|
Set to +5 ---------| ----------
optocoupler


Is this a safe way to do things? Seems to me that in theory, when Q1 turns
on (due to signal from the other side of the optocoupler) the Error line
will be pulled low to gnd, and D0 is sourcing < 1 mA (safe). When Q1 is
off, Error is pulled to the same level as D0 (high). I think this is proper
for TTL, but I wanted to check before I damaged my motherboard

 

I've got a page below that does something similar with the
parallel port, using qbasic and a web server to check the status
of some switches. I used transistors to pull the status lines low
enough to show a change of state. Using the transistors and 4.7k
resistors, the data lines can supply enough current to make the
setup work.

http://www.geocities.com/zoomkat/status.htm
http://zoomkat.d2g.com:88/cgi/status.bat