[comp.unix.i386] Parallel I/O Port

raj@cbnewsl.ATT.COM (Richard A. Johnson) (08/25/89)

I have an AT&T 6386 WGS running UNIX.  I want to use the parallel I/O
port to communicate with devices other than printers.  One example
would be to connect 2 PCs together using the parallel port on each PC.

According to the man page for lp(7), "The parallel port behaves as
described in termio(7)."  From this I would assume that I can do what
I want to do, but I don't know how I need to connect the physical ports
together.  I tried 25-pin ribbon cables, and ran "cat /dev/lp" on one
PC, and "date > /dev/lp" on the other, but both commands hung.

Does anybody know how to do this?  I was thinking that perhaps I need
to switch some of the signals around in the connection, somwhat like
an RS232 null-modem connector.  Please send me mail if you can help.

Rich Johnson
AT&T Bell Labs
Whippany, NJ
att!video!raj

buck@siswat.UUCP (A. Lester Buck) (08/25/89)

In article <1609@cbnewsl.ATT.COM>, raj@cbnewsl.ATT.COM (Richard A. Johnson) writes:
> 
> I have an AT&T 6386 WGS running UNIX.  I want to use the parallel I/O
> port to communicate with devices other than printers.  One example
> would be to connect 2 PCs together using the parallel port on each PC.

The best discussion of PC parallel ports I have ever seen was in an
article in MicroCornucopia magazine, #38, Nov-Dec 87, p.28, entitled
"Magic in the Real World" by Bruce Eckel.  He gives a complete and
detailed schematic for a $19 parallel port card, shows the small
hardware modification necessary to make it bidirectional, and covers
the tricks of using the status lines to transmit data without hardware
modifications.  You won't be able to use the standard lp driver to
transfer data bi-directionally.  The article also gives Turbo C code
for a TSR that manipulates the parallel port.  You might use this
as the basis for a new lp driver for data transfer.

-- 
A. Lester Buck		...!texbell!moray!siswat!buck